Process for producing 2,2'-Bis(hydroxymethyl) alkanoic acid

A process for producing 2,2'-bis(hydroxymethyl)alkanoic acid of the present invention, comprises: PA1 a 2,2'-bis(hydroxymethyl)alkanal production step (A1) of reacting aliphatic aldehyde having two hydrogen atoms bonded to .alpha.-carbon atom thereof, with formaldehyde in the presence of a water-soluble base; PA1 a 2,2'-bis(hydroxymethyl)alkanoic acid production step (B) of subjecting the thus obtained aqueous solution (a) containing 2,2'-bis(hydroxymethyl)alkanal and the base to oxidation treatment; and PA1 an alkanoic acid recovery step (C) of separating 2,2'-bis(hydroxymethyl)alkanoic acid from the thus obtained aqueous solution (b) containing the 2,2'-bis(hydroxymethyl)alkanoic acid and the base, PA1 in the alkanoic acid recovery step (C), a mineral acid being added to the aqueous solution (b) in an amount of not more than one equivalent based on the base in the aqueous solution (b) to convert the base into a salt thereof, PA1 water in the aqueous solution (b) being replaced with an organic solvent to form an organic solvent solution, and after removing the mineral acid salt precipitated from the organic solvent solution, 2,2'-bis(hydroxymethyl)alkanoic acid being crystallized from the organic solvent solution.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for producing 
2,2'-bis(hydroxymethyl)alkanoic acid, and more particularly to, an 
industrially useful process for producing 2,2'-bis(hydroxymethyl)alkanoic 
acid, which process includes an improved step for recovery of the alkanoic 
acid. The 2,2'-bis(hydroxymethyl)alkanoic acid (hereinafter referred to 
merely as "dimethylol alkanoic acid") can be produced by the oxidation of 
2,2'-bis(hydroxymethyl)alkanal (hereinafter referred to merely as 
"dimethylol alkanal"), and is useful as a raw material for the production 
of polyesters, polyurethanes, alkyd resins or the like. 
The dimethylol alkanal can be obtained by condensation-reacting aliphatic 
aldehyde having two hydrogen atoms bonded to .alpha.-carbon atom thereof, 
with an appropriate amount of formaldehyde in the presence of a base 
(refer to the following reaction formula (I)). Upon the condensation 
reaction, 2-substituted acrolein is by-produced. Alternatively, the 
dimethylol alkanoic acid can be produced by the oxidation of dimethylol 
alkanal (refer to the following reaction formula (II)). The by-produced 
2-substituted acrolein is converted into dimethylol alkanal by reacting 
with an appropriate amount of formaldehyde in the presence of a base 
(refer to the following reaction formula (III)). 
##STR1## 
As the bases (condensation catalysts) used in the production of dimethylol 
alkanal, there have been proposed sodium hydroxide (Japanese Patent 
Publication (KOKOKU) No. 52-20965(1977) and Japanese Patent Application 
Laid-open (KOKAI) No. 62-263141(1987)), sodium carbonate (U.S. Pat. No. 
3,312,736), triethylamine (Japanese Patent Publication (KOKOKU) No. 
4-55181(1992)), dimethylamino neopentanol (German Patent No. 2,507,461) or 
the like. 
Specifically, for example, in U.S. Pat. No. 3,312,736, there is described a 
process in successive steps from the production of dimethylol alkanal to 
the recovery of dimethylol alkanoic acid, comprising reacting n-butyl 
aldehyde with formaldehyde in a water solvent in the presence of sodium 
carbonate, treating the reaction solution with hydrogen peroxide, removing 
inorganic substances derived from sodium carbonate, from the reaction 
solution using sulfonate-type cation exchange resin, subjecting the 
reaction solution to evaporation treatment, and cooling and then filtering 
the reaction solution to obtain 2,2'-bis(hydroxymethyl)butanoic acid as a 
solid. 
However, in the above-mentioned conventional process, a large amount of 
wash water is required to regenerate the cation exchange resin, so that a 
large amount of waste water must be treated subsequently, which is 
extremely disadvantageous from the industrial viewpoint. 
As a result of the present inventors' studies, it has been found that in an 
alkanoic acid recovery step, by adding a mineral acid to an aqueous 
solution containing the 2,2'-bis(hydroxymethyl)alkanoic acid and the base, 
in an amount of not more than one equivalent based on the base in the 
aqueous solution to convert the base into a salt thereof; adding an 
organic solvent to the aqueous solution to replace water in the aqueous 
solution with an organic solvent, thereby forming an organic solvent 
solution; and after removing the mineral acid salt precipitated from the 
obtained organic solvent solution, crystallizing 
2,2'-bis(hydroxymethyl)alkanoic acid from the organic solvent solution, 
2,2'-bis(hydroxymethyl)alkanoic acid can be recovered in a high yield. The 
present invention has been attained in the basis of the finding. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an industrially useful 
process for producing 2,2'-bis(hydroxymethyl)alkanoic acid, which process 
includes an improved step for the recovery of 
2,2'-bis(hydroxymethyl)alkanoic acid. 
It is another object of the present invention to provide a process for 
producing 2,2'-bis(hydroxymethyl)alkanoic acid, which process is capable 
of reducing a load for recovering unreacted formaldehyde and decreasing an 
amount of residual formaldehyde, thereby producing 
2,2'-bis(hydroxymethyl)alkanoic acid with a high yield. 
To accomplish the aim, in a first aspect of the present invention, there is 
provided a process for producing 2,2'-bis(hydroxymethyl)alkanoic acid, 
comprising: 
a 2,2'-bis(hydroxymethyl)alkanal production step (A1) of reacting aliphatic 
aldehyde having two hydrogen atoms bonded to .alpha.-carbon atom thereof, 
with formaldehyde in the presence of a water-soluble base; 
a 2,2'-bis(hydroxymethyl)alkanoic acid production step (B) of subjecting 
the thus obtained aqueous solution (a) containing 
2,2'-bis(hydroxymethyl)alkanal and the base to oxidation treatment; and 
an alkanoic acid recovery step (C) of separating 
2,2'-bis(hydroxymethyl)alkanoic acid from the thus obtained aqueous 
solution (b) containing the 2,2'-bis(hydroxymethyl)alkanoic acid and the 
base, 
in the alkanoic acid recovery step (C), a mineral acid being added to the 
aqueous solution (b) in an amount of not more than one equivalent based on 
the base in the aqueous solution (b) to convert the base into a salt 
thereof, water in the aqueous solution (b) being replaced with an organic 
solvent to form an organic solvent solution, and after removing the 
mineral acid salt precipitated from the organic solvent solution, 
2,2'-bis(hydroxymethyl)alkanoic acid being crystallized from the organic 
solvent solution.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is described in detail below. The process for 
producing dimethylol alkanoic acid comprises at least an alkanal 
production step (A1), an alkanoic acid production step (B) and an alkanoic 
acid recovery step (C). In the present invention, the alkanoic acid 
recovery step (C) comprising a crystallization method including a specific 
pre-treatment. 
In accordance with the first preferred embodiment of the present invention, 
the process further comprises an alkanoic acid re-recovery step (D) of 
adding an aqueous solution of inorganic base to an organic solvent 
solution recovered by liquid-solid separation after the crystallization 
and containing uncrystallized alkanoic acid, thereby converting the 
alkanoic acid into a salt thereof, and then eluting (distilling off) water 
from a water phase separated from the organic solvent solution, thereby 
recovering the alkanoic acid salt. 
In accordance with the second preferred embodiment of the present 
invention, the process further comprises an alkanal production step (A2) 
of reacting formaldehyde with 2-substituted acrolein by-produced in the 
alkanal production step (A1), in a water solvent in the presence of a 
water-soluble base. 
In addition, in accordance with the third preferred embodiment of the 
present invention, the process further comprises an acrolein separation 
step (E) of recovering a 2-substituted acrolein-rich component from the 
reaction solution of the alkanal production step (A1), and a 
2,2'-bis(hydroxymethyl)alkanal production step (A2) of reacting 
formaldehyde with the 2-substituted acrolein recovered in the acrolein 
separation step (E), in a water solvent in the presence of a water-soluble 
base. At least a part of the formaldehyde-containing reaction solution 
produced in the 2,2'-bis(hydroxymethyl)alkanal production step (A2), is 
circulated to the alkanal production step (A1). The respective steps of 
the third preferred embodiment may be conducted in a continuous manner. 
First, the alkanal production step (A1) is explained below. In the step 
(A1), an aliphatic aldehyde having two hydrogen atoms bonded to 
.alpha.-carbon atom thereof (hereinafter referred to merely as "aliphatic 
aldehyde"), is reacted with formaldehyde in a water solvent in the 
presence of a water-soluble base, thereby producing alkanal. 
Simultaneously, 2-substituted acrolein is by-produced in the step (A1). In 
FIG. 1, aliphatic aldehyde (1), formaldehyde (2) and a water-soluble base 
(condensation catalyst) (3) are supplied to the alkanal production step 
(A1). 
The aliphatic aldehyde used in the present invention is represented by the 
general formula: R--CH.sub.2 CHO, wherein R is a substituted or 
unsubstituted straight-chain or branched saturated alkyl group having 
usually 1 to 7 carbon atoms. Specific examples of the substituents R may 
include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, 
n-hexyl, n-heptyl, isohexyl or the like. Among these alkyl groups, methyl, 
ethyl, n-propyl and isopropyl are preferred. The substituents R are not 
particularly restricted as long as the substituents are inactive under the 
reaction conditions. Typical examples of the other substituents R than the 
above may include alkoxy groups having 1 to 4 carbon atoms, specifically, 
methoxy, ethoxy, propoxy and butoxy. 
The aliphatic aldehyde used in the present invention are aldehydes having 
two hydrogen atoms bonded to .alpha.-carbon atom thereof. Specific 
examples of the aliphatic aldehydes may include propionaldehyde, n-butyl 
aldehyde, isobutyl aldehyde, n-pentyl aldehyde, isopentyl aldehyde, 
n-hexyl aldehyde, isohexyl aldehyde, n-heptyl aldehyde, isoheptyl 
aldehyde, n-octyl aldehyde, isooctyl aldehyde, n-nonyl aldehyde, isononyl 
aldehyde or the like. In the case where the process includes the 
below-mentioned alkanal production step (A2) (the converting step of 
2-substituted acrolein into alkanal), there may be suitably used aliphatic 
aldehydes which can readily by-produce 2-substituted acrolein, namely 
aliphatic aldehydes in which the carbon number of R in the above general 
formula is not less than 2 (i.e., aliphatic aldehydes having a larger 
number of carbon atoms than that of propionaldehyde). 
It is preferred that the formaldehyde may be diluted with water and used in 
the form of an aqueous solution from the standpoint of handling property 
thereof. The concentration of formaldehyde is usually 5 to 60% by weight, 
preferably 30 to 55% by weight. 
As the water-soluble bases (condensation catalysts), there may be used 
various bases described, for example, in Japanese Patent Application 
Laid-open (KOKAI) Nos. 52-124213(1977) and 4-55181(1992), German Patents 
Nos. 947,419 and 2,507,461, U.S. Pat. No. 3,312,736 and British Patent No. 
1,317,106. Examples of these water-soluble bases may include hydroxides or 
carbonates of alkali metals, hydroxides or carbonates of alkali earth 
metals, tertiary amines or the like. These bases may be used in the form 
of a mixture of any two or more thereof. 
As the hydroxides or carbonates of alkali metals, there may be exemplified 
sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium 
hydroxide, potassium carbonate, potassium bicarbonate or the like. As the 
tertiary amines, there may be exemplified aliphatic, alicyclic or 
heterocyclic amines having usually 3 to 20 carbon atoms, preferably 3 to 
15 carbon atoms. Among these amines, the aliphatic tertiary amines are 
preferred. 
Specific examples of the aliphatic tertiary amines may include symmetrical 
trialkyl amines such as trimethyl amine, triethyl amine, tri-n-propyl 
amine, triisopropyl amine, tri-n-butyl amine, triisobutyl amine or 
tri-tert-butyl amine; unsymmetrical trialkyl amines such as methyldiethyl 
amine, dimethylethyl amine, ethyldiisopropyl amine or dimethyl-tert-butyl 
amine; diamines such as N,N-tetramethyl ethylene diamine or triethylene 
diamine; substituted amines such as N,N-dimethylcyclohexyl amine, 
bis(2-hydroxyethyl)cyclohexyl amine, N-methyl pyrrolidine, N-methyl 
piperidine, N-methyl morpholine, N,N-dimethylamino ethanol or 
N,N-dimethylamino neopentanol; aromatic ring-containing amines such as 
tribenzyl amine or N,N-dimethylbenzyl amine; tertiary amino 
group-containing polyamines such as triethylene diamine or 
bis(2-dimethylaminoethyl)methyl amine; tetra-alkyl ammoniums such as 
tetraethyl ammonium hydroxide; or the like. Among them, trialkyl amines 
are preferred. 
The dimethylol alkanals produced in the alkanal production step (A1) may 
include, for example, dimethylol propanal in the case where 
propionaldehyde is used as the raw aliphatic aldehyde, or dimethylol 
butanal in the case where n-butyl aldehyde is used as the raw aliphatic 
aldehyde. Specific examples of the 2-substituted acroleins (for example, 
2-alkyl acroleins) by-produced simultaneously may include 2-methyl 
acrolein, 2-ethyl acrolein, 2-propyl acrolein, 2-butyl acrolein, 2-pentyl 
acrolein, 2-hexyl acrolein or the like. The reaction conditions of the 
alkanal production step (A1) are described in detail hereinafter. 
Next, the acrolein separation step (E) is explained. In the step (E), a 
2-substituted acrolein-rich component is recovered from the reaction 
solution of the alkanal production step (A1). In FIG. 1, the reaction 
solution (4) of the alkanal production step (A1) is supplied to the 
acrolein separation step (E) where the reaction solution is separated into 
a 2-substituted acrolein-rich component (5) and a dimethylol alkanal-rich 
component (base-containing component) (6). The concentration of 
2-substituted acrolein in the component (5) is usually 30 to 100% by 
weight, preferably 50 to 100% by weight. On the other hand, the 
concentration of dimethylol alkanal in the component (6) is usually 10 to 
80% by weight, preferably 20 to 60% by weight. Specifically, as the 
separation methods, there may be exemplified a distillation method, a 
solvent extraction method or the combination of these methods which may be 
conducted in an appropriate order. Among them, the distillation method is 
preferred because of simplicity thereof. The component (5) may contain in 
addition to the 2-substituted acrolein, unreacted aliphatic aldehyde, 
formaldehyde, water, methanol and the base (condensation catalyst). 
Next, the alkanal production step (A2) is explained. In the step (A2), 
formaldehyde is reacted with the 2-substituted acrolein recovered in the 
acrolein separation step (E) in a water solvent in the presence of a 
water-soluble base. In FIG. 1, formaldehyde (2), the 2-substituted 
acrolein-rich component (5) and the base (condensation catalyst) (3) are 
supplied to the alkanal production step (A2), whereby 2-substituted 
acrolein is converted into dimethylol alkanal. At least a part of a 
formaldehyde-containing reaction solution (18) of the alkanal production 
step (A2) is circulated to the alkanal production step (A1) (In FIG. 1, a 
whole amount of the reaction solution (18) is circulated to the step 
(A1)). As the water-soluble base, there may be used the same bases as used 
in the alkanal production step (A1). Incidentally, kinds of bases used in 
the alkanal production steps (A1) and (A2) may be different from each 
other. The reaction conditions of the alkanal production step (A2) are 
described in detail hereinafter. 
Meanwhile, under such a condition that the molar ratio of formaldehyde to 
aliphatic aldehyde is 2:1 to 10:1 in the presence of the base, a 
considerable amount of the 2-substituted acrolein by-product is produced 
in addition to dimethylol alkanal. The amount of the 2-substituted 
acrolein by-product varies depending upon kind of the aldehyde used, kind 
and amount of the base used, the reaction temperature or the like. For 
example, in the case where n-butyl aldehyde and formaldehyde are reacted 
with each other at about 60.degree. C. in the presence of triethyl amine, 
2-ethyl acrolein is by-produced in an amount of about 20% by weight. 
Incidentally, it is known that the 2-substituted acrolein is produced by 
the dehydration reaction of 2-hydroxymethyl alkanal as a precursor of 
dimethylol alkanal, and that upon the dehydration reaction, the 
2-hydroxymethyl alkanal and the 2-substituted acrolein have an equilibrium 
relationship to each other. Accordingly, under such a condition that the 
molar ratio of formaldehyde to aliphatic aldehyde is small, it is 
inevitable to by-produce the 2-substituted acrolein. 
In the case where the molar ratio of formaldehyde to aliphatic aldehyde is 
more than 10:1, it is possible to suppress the production of the 
2-substituted acrolein by-product, and to produce dimethylol alkanal with 
a high yield. However, in this case, since an excessive amount of 
formaldehyde remains unreacted, complicated operations are required for 
separation or recycle of the residual formaldehyde, resulting in increase 
in costs therefor. Further, since an excessive amount of formaldehyde 
remains in dimethylol alkanal, it is required to add a large amount of 
expensive oxidants in the subsequent oxidation step, and there also arises 
a problem that side reactions tend to be induced. 
On the other hand, the 2-substituted acrolein may be converted into 
dimethylol alkanal by reacting with formaldehyde in the presence of the 
base and water. As such a conversion method, there have been proposed the 
following methods. 
In Japanese Patent Application Laid-open (KOKAI) No. 52-124213(1977), there 
has been described a method of reacting 2-ethyl acrolein with an aqueous 
formaldehyde solution in the presence of triethyl amine, thereby obtaining 
dimethylol butanal. However, in this method, in order to enhance the 
reaction efficiency, formaldehyde must be used in an extremely excess 
amount based on the weight of the 2-substituted acrolein. Therefore, it is 
required to remove an excess amount of residual formaldehyde, which is 
industrially disadvantageous. 
In German Patent No. 2,507,461, there has been proposed a method of 
reacting n-butyl aldehyde with formaldehyde, for example, in the presence 
of N,N-dimethylamino neopentanol in a first stage reactor, separating 
unreacted n-butyl aldehyde and by-produced 2-ethyl acrolein from the 
reaction solution by a distillation method, and adding formaldehyde and 
amine to the obtained distillate to conduct a second stage reaction. 
However, in this method, since formaldehyde is used in a stoichiometric 
amount, the yield of dimethylol alkanal is low. 
As methods of producing dimethylol alkanoic acid by the oxidation of 
dimethylol alkanal, there are known an oxidation method using hydrogen 
peroxide (e.g., U.S. Pat. No. 3,312,736), an oxidation method using 
hydrogen peroxide and a catalyst composed of at least one element selected 
from the group consisting of cerium, titanium, zirconium, tin, niobium, 
molybdenum and tungsten (Japanese Patent Application Laid-open (KOKAI) No. 
62-263141(1987)), an oxidation method using perisobutyric acid (Journal of 
Synthetic Organic Chemistry Japan, 36, 1095(1978)), or the like. 
However, in any of the above-mentioned known methods, the yield of 
dimethylol alkanal is low, and when the dimethylol alkanal produced is 
oxidized, a large amount of oxidant is required since the amount of 
residual formaldehyde is large. Therefore, it is not possible to obtain 
the aimed product with a high purity and a high yield. 
As described above, conventionally, there are not known any method capable 
of producing dimethylol alkanal with a high yield, and capable of 
decreasing an amount of residual formaldehyde. 
In consequence, from the standpoints of reducing a load required for the 
recovery of unreacted formaldehyde, decreasing the amount of residual 
formaldehyde and producing dimethylol alkanal with a high yield, in 
accordance with the third preferred embodiment of the present invention, 
it is preferred that the molar ratio (I) of formaldehyde to aliphatic 
aldehyde throughout the alkanal production steps (A1) and (A2) is adjusted 
to 1:1 to 1:5, and the molar ratio (II) of formaldehyde to 2-substituted 
acrolein in the alkanal production step (A2) is adjusted to 1:3 to 1:100. 
Further, from the standpoint of reducing the amount of formaldehyde 
remaining in dimethylol alkanal, it is more preferred that the molar ratio 
(I) is 1:1 to 1:3 and the molar ratio (II) is 1:3 to 1:50. 
The molar ratio of 2-substituted acrolein by-produced to aliphatic aldehyde 
charged in the alkanal production step (A1) is influenced by a molar ratio 
between formaldehyde and aliphatic aldehyde charged. Therefore, the molar 
ratio between 2-substituted acrolein and aliphatic aldehyde present in the 
alkanal production step (A1) is adjusted to preferably 1:0.01 to 1:2, more 
preferably 1:0.05 to 1:1. Under the condition that the amount of 
2-substituted acrolein by-produced is small, the amount of dimethylol 
alkanal converted from the 2-substituted acrolein also becomes small, so 
that the aims of the third preferred embodiment of the present invention 
cannot be sufficiently accomplished. Further, when the amount of 
2-substituted acrolein produced is small, the amount of formaldehyde used 
based on aliphatic aldehyde is necessarily increased, so that there is 
caused such an industrial disadvantage that a load required for the 
removal of excessive formaldehyde becomes large. 
The amount of the base used in the alkanal production step (A1) is usually 
0.01 to 1.0 mol, preferably 0.02 to 0.5 mol based on 1 mol of aliphatic 
aldehyde. In addition, the amount of the base used in the alkanal 
production step (A2) is usually 0.01 to 1.0 mol, preferably 0.02 to 0.5 
mol based on 1 mol of 2-substituted acrolein. 
The reaction temperatures of the respective steps vary depending upon kind 
and amount of the base used. For example, when hydroxides of alkali metals 
or alkali earth metals are used, the reaction temperature is usually -10 
to 100.degree. C., preferably 10 to 80.degree. C. When tertiary amines are 
used, the reaction temperature is usually -10 to 120.degree. C., 
preferably 10 to 100.degree. C. These reactions may be conducted not only 
under ordinary pressure but also under reduced or increased pressure. 
Next, the alkanoic acid production step (B) is explained. In the step (B), 
the aqueous solution (a) containing dimethylol alkanal and a base is 
subjected to oxidation treatment, thereby obtaining alkanoic acid. In FIG. 
1, the base-containing aqueous solution (6) of the dimethylol alkanal-rich 
component recovered in the acrolein separation step (E), and the oxidant 
(7) are supplied to the alkanoic acid production step (B). In the step 
(B), dimethylol alkanoic acid is produced by the oxidation of dimethylol 
alkanal. 
As the oxidation method, there may be used the above-mentioned known 
methods, namely an oxidation method using hydrogen peroxide (e.g., U.S. 
Pat. No. 3,312,736), an oxidation method using hydrogen peroxide in the 
presence of a catalyst composed of at least one element selected from the 
group consisting of cerium, titanium, zirconium, tin, niobium, molybdenum 
and tungsten (Japanese Patent Application Laid-open (KOKAI) No. 
62-263141(1987)), an oxidation method using perisobutyric acid (Journal of 
Synthetic Organic Chemistry Japan, 36, 1095(1978)), or the like. Among 
these methods, the oxidation method using hydrogen peroxide is preferred. 
The hydrogen peroxide may be used in the form of an aqueous solution 
containing hydrogen peroxide in an amount of usually 20 to 60% by weight. 
The amount of hydrogen peroxide used is usually 0.2 to 2 mol, preferably 
0.4 to 1.5 mol based on 1 mol of dimethylol alkanal. The concentration of 
dimethylol alkanal in the oxidation reaction system is usually 5 to 60% by 
weight, preferably 20 to 50% by weight. The oxidation reaction temperature 
is usually 20 to 100.degree. C., preferably 40 to 80.degree. C. The above 
oxidation reaction is continued until no unreacted dimethylol alkanal 
remains in the reaction system. 
Next, the alkanoic acid recovery step (C) is explained. In the step (C), 
dimethylol alkanoic acid is separated from the aqueous solution (b) 
containing the dimethylol alkanoic acid and the base. More specifically, a 
mineral acid is added to the above aqueous solution (b) such that the 
amount of the mineral acid added is not more than one equivalent based on 
the base (condensation catalyst) in the aqueous solution (b), thereby 
converting the base into a salt thereof. Successively, water in the 
aqueous solution (b) is replaced with an organic solvent, and after the 
mineral acid salt precipitated is removed, alkanoic acid is crystallized 
from the organic solvent solution. 
According to the above crystallization method including the specified 
pre-treatment, it is possible to readily separate dimethylol alkanoic acid 
and the base converted into the mineral acid salt, from the aqueous 
solution containing the dimethylol alkanoic acid and the base which have a 
high water-solubility. In FIG. 1, the aqueous solution (8), the mineral 
acid (9) and the organic solvent (10) are supplied to the alkanoic acid 
recovery step (C), and water (11) and the mineral acid salt (12) are 
removed from the alkanoic acid recovery step (C). Further, the reaction 
mixture of the alkanoic acid recovery step (C) is subjected to 
liquid-solid separation, thereby separating the reaction mixture into 
dimethylol alkanoic acid crystals (13) and the organic solvent solution as 
a mother liquor (filtrate) (14). 
As the mineral acids, there may be exemplified hydrochloric acid, sulfuric 
acid, nitric acid, phosphoric acid or the like. Among them, sulfuric acid 
is preferred. The amount of the mineral acid used is not more than one 
equivalent, preferably 0.85 to 1 equivalent based on one equivalent of the 
base (condensation catalyst) in the aqueous solution (b). When the amount 
of the mineral acid added is more than one equivalent, residual formic 
acid and hydroxymethyl groups are esterified together, so that the yield 
of dimethylol alkanoic acid is decreased. On the other hand, when the 
amount of the mineral acid added is too small, the salt of dimethylol 
alkanoic acid and base tends to be disadvantageously incorporated into the 
dimethylol alkanoic acid crystals. 
As the methods of replacing water in the aqueous solution (b) with an 
organic solvent, there may be exemplified a method comprising distilling 
off a large portion of water in the aqueous solution (b) and then adding 
an organic solvent to the distillation residue; a method comprising adding 
an organic solvent to the aqueous solution (b) to cause phase-separation 
of the solution, and then removing a water phase therefrom; or the like. 
Further, as the method comprising distilling off water from the aqueous 
solution (b), there may be adopted a method of heating the aqueous 
solution (b) under reduced pressure, thereby distilling off water 
therefrom; a method comprising adding an organic solvent to the aqueous 
solution (b) and then evaporating water together with the organic solvent; 
or the like. In case of distilling off water, it is preferred that the 
degree of reduced pressure is controlled such that the temperature of the 
aqueous solution (b) is maintained at usually not more than 100.degree. 
C., preferably not more than 80.degree. C. When the temperature of the 
aqueous solution (b) is too high, the dehydration-condensation of 
dimethylol alkanoic acid tends to be caused, thereby producing an 
anhydride thereof, and further residual formic acid is reacted with 
methylol groups of dimethylol alkanoic acid, so that the yield of 
dimethylol alkanoic acid is decreased. 
Kinds of organic solvents used are not particularly restricted as long as 
salts formed by the mineral acid and base (condensation catalyst) is 
insoluble therein but dimethylol alkanoic acid is soluble therein. For 
example, in the case of using dimethylol alkanoic acids other than 
dimethylol propionic acid, examples of suitable organic solvents may 
include aliphatic ketones such as acetone, methyl ethyl ketone or methyl 
isobutyl ketone; aliphatic esters such as ethyl acetate, propyl acetate, 
butyl acetate or isobutyl acetate; aliphatic nitrites such as acetonitrile 
or propionitrile; or the like. On the other hand, in the case of using 
dimethylol propionic acid, examples of suitable organic solvents may 
include alcohols such as methanol, ethanol, propanol or isopropyl alcohol, 
or the like. 
In the case where dialkyl ketone is used as the above organic solvent, the 
following advantages can be attained. Namely, there can be produced 
alkanoic acid crystals which have a narrow particle size distribution and 
a small particle size and, therefore, are excellent in solubility and 
handling property upon dissolving, when used as raw materials for the 
production of polyesters, polyurethanes, alkyd resins or the like. 
Specific examples of the dialkyl ketones may include acetone, methyl ethyl 
ketone, diethyl ketone, methyl n-propyl ketone, methyl isopropyl ketone, 
methyl n-butyl ketone, methyl isobutyl ketone, di-n-propyl ketone, 
diisopropyl ketone, ethyl n-propyl ketone, ethyl n-butyl ketone, ethyl 
isobutyl ketone, methyl n-amyl ketone, methyl isoamyl ketone, diisobutyl 
ketone or the like. Among these dialkyl ketones, acetone is rather 
disadvantageous, because acetone has a too large solubility in water so 
that the recovery thereof becomes difficult. From such a standpoint, 
unsymmetrical dialkyl ketones are preferred. Further, in view of costs, 
methyl isobutyl ketone is more preferred. 
The amount of the organic solvent used is usually 1 to 10 times, preferably 
1.5 to 5 times based on the weight of dimethylol alkanoic acid. When the 
amount of the organic solvent used is too large, the amount of dimethylol 
alkanoic acid dissolved therein is increased so that the percentage of 
crystallization thereof is decreased. On the other hand, when the amount 
of the organic solvent used is too small, the purity of dimethylol 
alkanoic acid produced is lowered. 
When the mineral acid salt is removed from the solution whose solvent is 
replaced with the organic solvent, it is preferred to control the amount 
of water in the organic solvent solution as follows. Namely, the amount of 
water in the organic solvent solution is adjusted to usually not more than 
5% by weight, preferably not more than 1% by weight in the case of using 
dimethylol alkanoic acids other than dimethylol propionic acid, or usually 
not more than 10% by weight, preferably not more than 5% by weight in the 
case of using dimethylol propionic acid. In the case where the amount of 
water is not controlled to such a range, there arises such a tendency that 
the mineral acid salt is dissolved in water and disadvantageously 
incorporated in the crystallized dimethylol alkanoic acid. 
When the mineral acid salt precipitated from the organic solvent solution 
is removed by filtration, too low temperature of the organic solvent 
solution may cause crystallization of dimethylol alkanoic acid upon the 
filtration, so that the recovery efficiency of dimethylol alkanoic acid 
becomes low. Therefore, upon the filtration, the organic solvent solution 
is preferably maintained at such a temperature at which dimethylol 
alkanoic acid can be kept dissolved therein. 
After the mineral acid salt is filtered out, the obtained filtrate is 
cooled for crystallization, whereby dimethylol alkanoic acid can be 
obtained in the form of crystals. The cooling temperature is usually 30 to 
-10.degree. C., preferably 10 to -5.degree. C. Upon the crystallization of 
dimethylol alkanoic acid, it is preferred that the amount of water in the 
organic solvent solution be adjusted to not more than 20% by weight based 
on the weight of the alkanoic acid. When the amount of water in the 
organic solvent solution is too large, the percentage of crystallization 
of dimethylol alkanoic acid is decreased. Further, under such a condition, 
since the crystallization temperature of dimethylol alkanoic acid becomes 
lowered, it is necessary to cool the organic solvent solution up to a 
lower temperature, resulting in disadvantages such as energy loss. The 
amount of water in the organic solvent solution is preferably not more 
than 10% by weight. Such a control of the amount of water in the organic 
solvent solution can be achieved by conducting the water 
amount-controlling treatment as described above with respect to the 
removal of mineral acid salt. Incidentally, when any mineral acid salt 
remains in the obtained crystals, the crystals are dissolved again in an 
organic solvent while heating. The obtained organic solvent solution is 
filtered while being kept in a hot condition, and then the resultant 
filtrate is subjected to recrystallization, whereby it is possible to 
remove a large portion of residual mineral acid salt. 
Next, the alkanoic acid re-recovery step (D) is explained. In the step (D), 
an aqueous solution of inorganic base is added to the organic solvent 
solution (filtrate) recovered by solid-liquid separation after the 
crystallization in the above-mentioned alkanoic acid recovery step (C) and 
containing uncrystallized alkanoic acid, thereby converting the alkanoic 
acid into a salt thereof. Then, water is distilled off from a water phase 
separated from the organic solvent solution, thereby recovering the 
alkanoic acid salt. Namely, dimethylol alkanoic acid of usually 5 to 8% by 
weight is dissolved in the filtrate obtained in the alkanoic acid recovery 
step (C) and such dimethylol alkanoic acid is present in the form of a 
mixed solution with impurities, so that it is not possible to recover the 
dimethylol alkanoic acid merely by distilling off the solvent. 
In consequence, in accordance with the present invention, an inorganic base 
is added to the above-mentioned filtrate to convert dimethylol alkanoic 
acid into a salt thereof, and then the resultant dimethylol alkanoic acid 
salt is separated and recovered from the filtrate. In FIG. 1, the filtrate 
(14) recovered from the alkanoic acid recovery step (C) and the aqueous 
solution (15) containing an inorganic base are supplied to the alkanoic 
acid re-recovery step (D). An organic phase (16) obtained by phase 
separation and water (17) distilled off from a water phase separated from 
the organic phase, are removed from the alkanoic acid re-recovery step 
(D), thereby recovering the dimethylol alkanoic acid salt (19). 
As the inorganic bases, there may be suitably used bases composed of alkali 
metals or alkali earth metals, such as hydroxides of alkali metals, 
carbonates of alkali metals, hydroxides of alkali earth metals, carbonates 
of alkali earth metals or the like. 
As the hydroxides of alkali metals, there may be exemplified sodium 
hydroxide, potassium hydroxide, lithium hydroxide or the like. As the 
carbonates of alkali metals, there may be exemplified sodium carbonate, 
potassium carbonate, lithium carbonate or the like. In addition, as the 
hydroxide of alkali earth metals, there may be exemplified calcium 
hydroxide, barium hydroxide or the like. As the carbonates of alkali earth 
metals, there may be exemplified calcium carbonate, barium carbonate or 
the like. 
The above inorganic base is added together with water to the filtrate. The 
inorganic base may be used in such an amount that when added together with 
water, the pH of the filtrate is adjusted to usually 8 to 10, preferably 
8.5 to 9.5. The temperature of the filtrate, when the inorganic base is 
added thereto, is usually 0 to 100.degree. C., preferably 20 to 50.degree. 
C. By stirring the filtrate, the dimethylol alkanoic acid salt in the form 
of an aqueous solution or solid is transferred to a water layer side and 
recovered therefrom. In the case where the dimethylol alkanoic acid salt 
is recovered in the form of an aqueous solution, water is distilled off 
from the aqueous solution, and if required, after a solvent in which the 
dimethylol alkanoic acid salt is less soluble, is added to the aqueous 
solution, the resultant solution is cooled and subjected to 
crystallization, whereby it is possible to recover the dimethylol alkanoic 
acid salt in the form of powder. 
In the case where it is required to take out a dimethylol alkanoic acid 
salt powder after the alkanoic acid has been recovered in the form of an 
aqueous solution, water is distilled off or evaporated from the aqueous 
solution at a temperature of 50 to 100.degree. C. under ordinary pressure 
or reduced pressure. In this case, it is preferred that the amount of 
water in the distillation residue be adjusted to usually not more than 10% 
by weight, preferably not more than 2% by weight, because the dimethylol 
alkanoic acid salt is extremely readily soluble in water. After distilling 
off water, alcohols such as methanol, ethanol, propanol or isopropanol may 
be added to the dimethylol alkanoic acid salt to form a dispersion 
thereof, followed by filtering the dispersion, whereby it is possible to 
obtain the dimethylol alkanoic acid salt in the form of powder. 
The production process according to the present invention may be conducted 
in a continuous manner by referring to the process shown in FIG. 1, but 
may also be conducted in a batch or semi-continuous manner. When the 
process is conducted in a limited scale, the batch or semi-continuous 
process is more suitable. Especially, it is preferred that steps 
subsequent to the alkanoic acid recovery step (C) are conducted in a batch 
manner. 
As described above, in accordance with the present invention, there is 
provided an industrially useful process for producing 
2,2'-bis(hydroxymethyl)alkanoic acid, which process includes an improved 
step for recovery of the 2,2'-bis(hydroxymethyl)alkanoic acid. Further, in 
the process according to the present invention, a load required for 
recovery of unreacted formaldehyde can be reduced, and the amount of 
residual formaldehyde can be decreased, thereby obtaining the 
2,2'-bis(hydroxymethyl)alkanoic acid with a high yield. Accordingly, the 
present invention is industrially valuable. 
EXAMPLES 
The present invention will now be described in more detail with reference 
to the following examples, but the present invention is not restricted to 
those examples and various modifications are possible within the scope of 
the invention. 
Example 1 
Alkanal Production Step (A1) 
72 g (1 mol) of n-butyl aldehyde and 98 g (1.7 mols) of an aqueous 52 wt. % 
formaldehyde solution were charged into a reactor, and 10.6 g (0.08 mol) 
of an aqueous 30 wt. % NaOH solution was dropped into the mixed solution 
while heating the solution to 40.degree. C. Thereafter, the mixed solution 
was reacted at a liquid temperature of 60.degree. C. for one hour. At this 
time, the molar ratio between n-butyl aldehyde, formaldehyde and NaOH 
charged was 1:1.7:0.08. 
The percentage of conversion of n-butyl aldehyde was 94 mol %; the total 
yield of dimethylol butanal and formaldehyde adducts of dimethylol butanal 
was 40 mol %; and the total selectivity of dimethylol butanal and 
formaldehyde adducts of dimethylol butanal was 43 mol %. Here, the 
formaldehyde adducts of dimethylol butanal are components which can be 
converted into dimethylol butanoic acid as an aimed product. Further, the 
yield of 2-ethyl acrolein was 23 mol %, and the amount of residual 
formaldehyde was 20 mol % based on the mole of n-butyl aldehyde. 
Acrolein Separation Step (E) 
Successively, the reaction solution of the alkanal production step (A1) was 
distilled at 90.degree. C. under ordinary pressure, thereby obtaining 23 g 
of a 2-ethyl acrolein-rich fraction (containing 79% by weight of 2-ethyl 
acrolein and 21% by weight of n-butyl aldehyde) from a top of the reactor, 
and 158 g of a dimethylol butanal-rich fraction (an aqueous 33 wt. % 
dimethylol butanal solution) from the bottom of the reactor. 
Alkanal Production Step (A2) 
The fraction (containing 17 g (0.2 mol) of 2-ethyl acrolein) from the 
acrolein separation step (E) was then added to 98 g (1.7 mols) of an 
aqueous 52 wt. % formaldehyde solution, and while heating the obtained 
solution to 40.degree. C., 2.7 g (0.02 mol) of an aqueous 30 wt. % NaOH 
solution was dropped thereinto. Thereafter, the liquid temperature of the 
obtained solution was maintained at 40.degree. C. for one hour, thereby 
reacting 2-ethyl acrolein and formaldehyde. At this time, the molar ratio 
between 2-ethyl acrolein, formaldehyde and NaOH charged was 1:8.5:0.1. 
The total yield of dimethylol butanal and formaldehyde adducts of 
dimethylol butanal was 70 mol % based on the mole of 2-ethyl acrolein. 
Further, the amount of residual formaldehyde was 140 mol % based on the 
mole of n-butyl aldehyde. 
Second Alkanal Production Step (A1) 
Next, 72 g (1 mol) of n-butyl aldehyde were added to the reaction solution 
obtained in the alkanal production step (A2) while maintaining at a 
temperature of 60.degree. C., and 8 g (0.06 mol) of an aqueous 30 wt. % 
NaOH solution was dropped into the obtained solution, thereby reacting 
n-butyl aldehyde with unreacted formaldehyde at 40.degree. C. for one 
hour. This reaction step can be regarded as such a case where the reaction 
solution obtained in the alkanal production step (A2) was used as a 
formaldehyde component in the above alkanal production step (A1). 
The percentage of conversion of n-butyl aldehyde in the second alkanal 
production step (A1) (based on the charged amount) was 78 mol %; the total 
yield of dimethylol butanal and formaldehyde adducts of dimethylol butanal 
(based on the charged amount) was 53 mol %; and the total selectivity of 
dimethylol butanal and formaldehyde adducts of dimethylol butanal (based 
on the charged amount) was 68 mol %. In addition, the yield of 2-ethyl 
acrolein was 20 mol % which was approximately the same as that in the 
first alkanal production step (A1). Further, the amount of residual 
formaldehyde was 19 mol % based on the mole of n-butyl aldehyde. 
The molar ratio between n-butyl aldehyde, 2-ethyl acrolein, formaldehyde 
and NaOH charged totally in the alkanal production step (A2) and the 
second alkanal production step (A1) was 1:0.2:1.7:0.8. Here, the molar 
ratio between 2-ethyl acrolein and formaldehyde totally charged expresses 
a molar ratio of the totally charged amount of 2-ethyl acrolein and 
formaldehyde in the alkanal production step (A2), to the charged amount of 
n-butyl aldehyde in the second alkanal production step (A1). 
When the same operations as defined above are repeated subsequently, it is 
considered that the above-mentioned molar ratio between n-butyl aldehyde, 
2-ethyl acrolein, formaldehyde and NaOH totally charged in the alkanal 
production steps (A1) and (A2) can be maintained, and the reaction 
therebetween can proceed in a stationary state. Thus, in the process 
comprising at least the alkanal production step (A1) and the alkanal 
production step (A2), an aimed product can be produced with a high yield 
even when the molar ratio of formaldehyde to n-butyl aldehyde totally 
charged is low. 
Alkanoic Acid Production Step (B) 
156 g of the fraction (an aqueous 46 wt. % alkanal solution) recovered from 
the bottom of a distillation tower in the acrolein separation step (E), 
was heated to 60.degree. C. After 51 g (0.52 mol) of an aqueous 35 wt. % 
hydrogen peroxide solution was dropped into the heated fraction for 2 
hours, the obtained mixture was further reacted for 5 hours. After 
completion of the oxidation reaction, the yield of dimethylol butanoic 
acid was 55 mol % based on the mole of n-butyl aldehyde consumed in the 
second alkanal production step (A1). 
Alkanoic Acid Recovery Step (C) 
7.9 g (0.038 mol; 0.95 equivalent based on NaOH) of an aqueous 47 wt. % 
sulfuric acid solution, was added to 200 g of the above-obtained oxidation 
reaction solution, thereby converting sodium derived from NaOH into sodium 
sulfate. Thereafter, water was distilled off from the reaction solution in 
a water bath maintained at 60.degree. C., under reduced pressure. After 90 
g of water was distilled off from the reaction solution, 208 g of methyl 
isobutyl ketone (MIBK) was added to the reaction solution, so that the 
amount of water in the reaction solution was adjusted to 0.7% by weight. 
Sodium sulfate precipitated with decrease in amount of water, was removed 
by filtration, and then the obtained filtrate was cooled to 0.degree. C., 
thereby precipitating crystals of dimethylol butanoic acid. The percentage 
of crystallization of dimethylol butanoic acid was 82% by weight. The 
yield of dimethylol butanoic acid is 45 mol % based on the mole of the 
converted n-butyl aldehyde excluding recovered n-butyl aldehyde. In 
addition, the Na concentration in the dimethylol butanoic acid crystals 
was 17 ppm, and the (SO.sub.4).sup.2- concentration therein was 6 ppm. The 
results are shown in Table 1. 
Examples 2 and 3 and Comparative Example 1 
The same procedure as defined in Example 1 was conducted except that the 
amount of sulfuric acid used in the alkanoic acid recovery step (C) 
(equivalent amount based on NaOH used as a condensation catalyst) was 
changed as shown in Table 1, thereby obtaining crystals of dimethylol 
butanoic acid. The results are shown in Table 1. 
TABLE 1 
______________________________________ 
Comparative 
Example 1 
Example 2 Example 3 
Example 1 
______________________________________ 
H.sub.2 SO.sub.4 /NaOH 
0.95 1.00 0.90 1.15 
equivalent 
Yield of 45 40 43 26 
dimethylol 
butanoic acid 
(mol %) (based on 
n-butyl aldehyde) 
Na concentration 
17 14 16 150 
in crystal (ppm) 
(SO.sub.4).sup.2- 
6 27 5 440 
concentration in 
crystal (ppm) 
______________________________________ 
Example 4 
Alkanal Production Step (A1) and Alkanoic Acid Production Step (B) 
73 g (1.2 mols) of propionaldehyde and 173 g (3 mols) of an aqueous 52 wt. 
% formaldehyde solution were charged into a reactor. While heating the 
obtained mixture to 25.degree. C., 48 g (0.09 mol) of an aqueous 20 wt. % 
Na.sub.2 CO.sub.3 solution was dropped thereinto for 2 hours. Thereafter, 
the reaction solution was heated to 70.degree. C. for 30 minutes, and 140 
g (1.44 mols) of an aqueous 35 wt. % hydrogen peroxide solution was 
dropped into the reaction solution for 4 hours. After completion of the 
dropping, the reaction solution was further stirred for 4 hours. 
Alkanoic Acid Recovery Step (C) 
Successively, 18.5 g (0.09 mol; 0.99 equivalent based on Na.sub.2 CO.sub.3) 
of an aqueous 47 wt. % sulfuric acid solution was added to the above 
reaction solution at 40.degree. C. Then, 244 g of water was distilled off 
from the reaction solution, under reduced pressure. Further, while 678 g 
of methanol was dropped into the thus-concentrated reaction solution, 
water remaining in the reaction solution was distilled off together with 
methanol therefrom at a temperature of 49 to 68.degree. C. under slightly 
reduced pressure. 294 g of methanol was further added to the obtained 
distillation residue. At this time, the amount of water in the obtained 
solution was 1.07% by weight. Further, the precipitation of crystals was 
observed in the solution, and the crystals precipitated was determined to 
be a mixture composed of sodium sulfate crystals and dimethylol propionic 
acid crystals. The solution was heated to 60 to 70.degree. C., thereby 
dissolving dimethylol propionic acid crystals therein. 
The above solution was filtered through a glass filter to remove sodium 
sulfate therefrom. The resultant filtrate was distilled and concentrated 
under slightly reduced pressure, thereby recovering 191 g of methanol. 
After 13 g of water and 33 g of methanol were added to the distillation 
residue to control the concentration thereof, the obtained solution was 
cooled to 0.degree. C. while stirring, so that dimethylol propionic acid 
crystals were precipitated. At this time, the yield of dimethylol 
propionic acid was 48 mol %. In addition, the Na concentration in the 
dimethylol propionic acid crystals was 78 ppm, and the (SO.sub.4).sup.2- 
concentration therein was 22 ppm. Further, when the above crystals were 
recrystallized from water, it was determined that the Na concentration in 
the crystals was 8.2 ppm, and the (SO.sub.4).sup.2- concentration therein 
was 6.2 ppm. The results are shown in Table 2. 
Examples 5 and 6 
The same procedure as defined in Example 4 was conducted except that the 
amount of sulfuric acid (equivalent amount based on Na.sub.2 CO.sub.3 used 
as a condensation catalyst) used in the alkanoic acid recovery step (C) 
was changed as shown in Table 2, thereby obtaining dimethylol propionic 
acid crystals. The results are shown in Table 2. 
Comparative Example 2 
The same procedure as defined in Example 4 was conducted except that the 
amount of sulfuric acid based on sodium carbonate used as a condensation 
catalyst was changed to 1.02 equivalents. Although it was attempted to 
obtain dimethylol butanoic acid crystals, a large portion of the obtained 
product was methyl dimethylol-propionate. The results are shown in Table 
2. 
TABLE 2 
______________________________________ 
Comparative 
Example 4 
Example 5 Example 6 
Example 2 
______________________________________ 
H.sub.2 SO.sub.4 /Na.sub.2 CO.sub.3 
0.99 0.97 0.95 1.02 
equivalent 
Yield of dimethylol 
48 46 44 4 
propionic acid 
(mol %) (based on 
propionaldehyde) 
Na concentration in 
78 190 170 -- 
crystal (ppm) 
(SO.sub.4).sup.2- 
22 10 23 -- 
concentration in 
crystal (ppm) 
Na concentration 
8 21 22 -- 
after 
recrystallization 
(ppm) 
(SO.sub.4).sup.2- 
6 8 7 -- 
concentration after 
recrystallization 
(ppm) 
______________________________________ 
Example 7 
The same procedure as defined in Example 1 was conducted except that a 
sodium salt of dimethylol butanoic acid was recovered from a filtrate from 
which dimethylol butanoic acid crystals have been separated by filtration, 
in the following manner, thereby producing dimethylol butanoic acid 
crystals. Specifically, 62 g of an aqueous 20 wt. % NaOH solution was 
dropped into the above filtrate containing dimethylol butanoic acid in an 
amount of 6% by weight (corresponding to 10 mol % based on the mole of the 
converted n-butyl aldehyde excluding recovered n-butyl aldehyde), and the 
solution was stirred. The pH of the solution was 9.0. 
Successively, the above solution was allowed to stand, whereby the solution 
was separated into two layers from which only a water layer as a lower 
layer was recovered. Water was distilled off from the recovered aqueous 
solution, under reduced pressure. When the amount of water in the 
distillation residue reached 1.2% by weight, 131 g of methanol was added 
to the distillation residue, and the resultant solution was heated to 
65.degree. C. while stirring, thereby dispersing a sodium salt of 
dimethylol butanoic acid therein. Thereafter, the resultant dispersion was 
cooled to 5.degree. C. and filtered to remove the sodium salt of 
dimethylol butanoic acid therefrom. The yield of the sodium salt of 
dimethylol butanoic acid was 9 mol % based on the mole of converted 
n-butyl aldehyde excluding recovered n-butyl aldehyde, and the percentage 
of recovery of the sodium salt of dimethylol butanoic acid from the 
filtrate was 93% by weight. 
Meanwhile, in order to determine what effects were obtained due to 
difference in kinds of organic solvents used upon crystallization, the 
following experiments were conducted. 
First, dimethylol butanoic acid crystals recovered in Example 1 were spread 
over a batt and dried at 60.degree. C. for 24 hours under reduced 
pressure. The obtained dry crystals were passed through a sieve to measure 
a particle size distribution thereof, and were tested to determine 
solubility thereof in various solvents. Further, the same procedure as 
defined in Example 1 was conducted except that the organic solvent used 
upon crystallization was changed from MIBK to ethyl acetate, thereby 
producing dimethylol butanoic acid crystals. The thus-obtained crystals 
were subjected to the same experiments as above. The results of 
measurements concerning a particle size distribution are shown in Table 3, 
and the results of solubility tests are shown in Table 4. 
TABLE 3 
______________________________________ 
Particle size and wt. % 
Less More 
Crystallization 
than 1 1 to 4 to 10 to than 30 
solvent mm 4 mm 10 mm 30 mm mm 
______________________________________ 
Example 1 
MIBK 83.1 4.0 8.3 2.7 1.9 
Reference 
Ethyl acetate 
28.4 21.1 25.4 18.2 6.9 
Example 1 
______________________________________ 
TABLE 4 
______________________________________ 
Dissolving time (min.) 
Methyl 
Crystalliza- ethyl N-methyl 
Ethyl 
tion solvent Acetone ketone pyrrolidone 
acetate 
______________________________________ 
Example 1 
MIBK 20 25 50 300 
Comparative 
Ethyl acetate 
56 240 91 1,080 
Example 1 
______________________________________ 
As is apparent from Table 3, by using dialkyl ketone as a crystallization 
solvent, the obtained alkanoic acid crystals showed a sharper particle 
size distribution (less secondary coagulation) and a small particle size. 
As shown in Table 4, such alkanoic acid can be rapidly dissolved in 
various organic solvents.