Neopentyl glycol is made by reacting isobutyraldehyde with paraformaldehyde in the presence of a tertiary amine and one or more oxides of elements of Groups IB, IVA, IVB, VA, VB, VIB and VIII of the periodic table; then hydrogenating the resulting hydroxypivaldehyde-containing product.

TECHNICAL FIELD 
This invention relates to the manufacture of neopentyl glycol. In 
particular it relates to the manufacture of neopentyl glycol by reacting 
isobutyraldehyde with paraformaldehyde in the presence of a catalyst 
comprising one or more oxides of elements of Groups IB, IVA, IVB, VA, VB, 
VIB and VIII of the periodic table and triethylamine or other lower alkyl 
tertiary amine, and hydrogenating the reaction product which includes 
hydroxypivaldehyde dimer. 
BACKGROUND ART 
Prior to this invention, it has been known to make neopentyl glycol (2,2 
dimethyl-1,3-dihydroxypropane, also known herein as NPG) by reacting 
formaldehyde with isobutyraldehyde and hydrogenating the resulting 
hydroxypivaldehyde (HPA). See U.S. Pat. No. 4,855,515, for example, which 
recites the historical development of the reaction and emphasizes the use 
of a particular catalyst in the hydrogenation step. U.S. Pat. No. 
3,808,280 discloses the use of triethylamine as a catalyst for the 
(aqueous) formaldehyde/isobutyraldehyde reaction. 
Each of the above references employs formaldehyde in the form of aqueous 
formaldehyde. 
Paraformaldehyde is used by Snam S.p.A. in UK Patent 1,017,618 to react 
with isobutyraldehyde in the presence of a tertiary amine to produce a 
reaction product containing apparently predominantly hydroxypivaldehyde 
which may be hydrogenated to neopentyl glycol. No reference to our 
knowledge teaches the use of one or more oxides of elements of Groups IB, 
IVA, IVB, VA, VB, VIB and VIII of the periodic table and paraformaldehyde 
with the accompanying advantages as explained below. Nor are we are of the 
use of metal oxide as a catalyst in such a reaction. 
SUMMARY OF THE INVENTION 
The present invention is a method of making hydroxypivaldehyde (HPA), and 
particularly its dimers, 
2-[1,1-dimethyl-2-hydroxy-methyl]-5,5-dimethyl-4-hydroxy-1,3-dioxane and 
subsequently neopentyl glycol (NPG), by reacting isobutyraldehyde (IBAL or 
2-methylpropanal) with paraformaldehyde in the presence of a tertiary 
amine catalyst, preferably triethylamine, and one or more oxides of 
elements of Groups IB, IVA, IVB, VA, VB, VIB and VIII of the periodic 
table (Chemical Rubber Company Handbook) to obtain HPA and HPA dimer, and 
hydrogenating the HPA and its dimer to obtain NPG. The HPA may be isolated 
in the form of the HPA dimer, which is a white solid: 
##STR1## 
The HPA is obtained at a faster rate and with a higher yield then in the 
presence of the metal oxide. Whether or not the HPA or its dimer is 
isolated and/or purified, they are conveniently hydrogenated a methanol 
solution, and in the presence of a copper chromite catalyst, for example, 
to obtain the desired neopentyl glycol. The HPA dimer hydrogenates as 
readily as HPA itself. 
A specific reaction may be described as follows: The reaction is performed 
in a reflux apparatus wherein one equivalent of isobutylraldehyde, 0.01 
equivalent of titanium dioxide, and about 0.04 to 0.05 equivalent of 
triethylamine have been placed under an inert atmosphere. Stir at the 
reflux temperature of isobutyraldehyde (about 63.degree.-64.degree. C.) 
until the isobutyraldehyde no longer refluxes, i.e. is consumed. The clear 
faintly yellow molten liquid obtained is decanted--or filtered from the 
titanium dioxide and gradually cooled to room temperature. 
Hydroxypivaldehyde dimer can be obtained by allowing it to precipitate and 
then washing to remove the amine catalyst, or crystallizing from a 
methanol solution. The HPA dimer, together with any residual HPA, is 
hydrogenated in any conventional (convenient) manner such as by passing a 
methanol solution over a copper chromite catalyst at about 150.degree. C. 
and about 2000 psi, to obtain the neopentyl glycol, which is finally 
purified by recrystallization and/or distillation. 
More generally, with one equivalent of isobutyraldehyde we may place in a 
reaction vessel from about 2 to about 0.1 equivalent of paraformaldehyde, 
about 0.001 to about 0.1 (preferably about 0.005 to about 0.05) equivalent 
of one or more oxides of elements of Groups IB, IVA, IVB, VA, VB, VIB and 
VIII of the periodic table and about 0.01 to about 0.1 (preferably 0.02 to 
about 0.08) equivalent of a tertiary amine. The reaction mixture is 
stirred under an argon purge until reflux of the isobutyraldehyde ceases. 
The resulting hydroxypivaldehyde and its dimer may be hydrogenated with 
out without further purification. 
As is known in the art, if the amine chosen has a boiling point lower than 
the boiling point (reflux temperature) of isobutyraldehyde, pressure may 
be used. 
Our invention provides a process in which water is not utilized and is 
therefore relatively easier to perform since it does not require the 
separation and/or disposal of water; the process is also considerably more 
efficient than prior art processes, since the HPA product can be used 
directly, i.e. without an arduous separation or purification process, for 
the hydrogenation step to NPG. However, if the product is to be stored, it 
is interesting to note that HPA dimer can be exposed to air indefinitely, 
as opposed to the monmer, which oxidizes rapidly to hydroxypivalic acid. 
The process is also more efficient in that fewer by-products are made, a 
high yield is obtained at a fast rate, and indeed one need not be 
concerned with the complications of by-products. Under properly controlled 
conditions, paraformaldehyde is easier and safer to store than aqueous 
formaldehyde. 
The metal oxide catalyst can be removed from the HPA reaction product 
before it is hydrogenated, by filtration or by any convenient means for 
recycling. The reaction may also be performed over a bed of catalyst. 
We may use various tertiary amines. Specifically, we may use as catalysts 
any tertiary amines of the general formula R.sup.1 R.sup.2 R.sup.3 N 
wherein R.sup.1, R.sup.2, and R.sup.3 are independently selected from 
alkyl and aryl groups of the general formula C.sub.1 -C.sub.15 and R.sup.1 
and R.sup.2 may form a substituted or unsubstituted cyclic group having 
from about 5 to about 15 carbon atoms.

DETAILED DESCRIPTION OF THE INVENTION 
Following are several examples of the invention: 
EXAMPLE 1 
In this experiment, isobutyraldehyde was converted to hydroxypivaldehyde 
dimer. 
Isobutyraldehyde (554.7 mmol), triethylamine (27.7 mmol), paraformaldehyde 
(527.0 mmol) and niobium oxide (5.6 mmol) were charged into a 250 ml rbf 
containing a magnetic stirbar and fitted with a reflux condenser. The rbf 
portion of the apparatus was submerged in a 80.degree. C. oil bath with 
magnetic stirring. The reaction was continued under an argon purge until 
the isobutyraldehyde no longer refluxed (generally about 1 to 3 hours) at 
which point the molten solution was allowed to slowly cool to room 
temperature. After the niobium oxide settled, the reaction mixture was 
decanted off and was allowed to stand at room temperature for about 2 
days. Solidification occurred (normally about 1 to about 3 days is 
required); the solid was recovered by suction filtration, pulverization, 
and washing with hexane. Hydroxypivaldehyde dimer (450 mmol) was observed 
as a white powder (m.p. 88.degree.-90.degree. C.) giving an isolated yield 
of 85% based on reacted paraformaldehyde; the HPA dimer was 92% pure by 
G.C. analysis. Higher purity dimer was obtained by recrystallization from 
methanol, and gave material melting at 106.degree.-108.degree. C. 
EXAMPLE 2 
Example 1 was repeated without niobium oxide, yielding 403 mmol of 
hydroxypivaldehyde dimer with a melting point of 84.degree.-86.degree. C. 
in 76% isolated yield based on reacted paraformaldehyde at 82% purity by 
G.C. analysis. 
EXAMPLE 3 
Hydroxypivaldehyde dimer made by the specific reaction described in the 
Summary of the Invention was dissolved in methanol to give 15.2% by weight 
solution. The solution was hydrogenated in an autoclave reaction over 
barium activated copper chromite at 150.degree. C. and 200 lb hydrogen 
pressure giving quantitative conversion of hydroxypivaldehyde to neopentyl 
glycol, i.e., &gt;99% purity was obtained as measured by gas chromatography 
without any special treatment such as the commonly used caustic 
purification treatment. 
Table I recites the results of experiments utilizing 
______________________________________ 
Reagent Equivalents 
______________________________________ 
IBAL 1.00 
Paraformaldehyde 
1.00 
Triethylamine 0.050 
Metal oxide 0.010 
______________________________________ 
The reactions were terminated 1 hour after the IBAL stopped refluxing and 
then analyzed by G.C. Everything else was done as similarly as possible so 
that the effect of the metal oxides could be compared. HPA selectivity was 
calculated as the monomer. 
TABLE I 
______________________________________ 
% % 
IBAL HPA % "44G" 
Reaction 
Co-Catalyst 
Conv. Sel. Sel.* Time (h) 
Comments 
______________________________________ 
1. None 92 92 3.7 2.42 Control 
2. Nb.sub.2 O.sub.5 
97 96 1.3 2.08 
3. ZrO.sub.2 98 97 1.0 2.00 
4. MnO.sub.2 97 90 7.3 1.92 
5. As.sub.2 O.sub.3 
97 97 1.3 2.00 
6. CuO 97 96 2.4 1.92 
7. TiO.sub.2 99 98 0.3 1.17 
8. CdO 97 66 29.0 1.08 
9. CeO.sub.2 97 94 0.6 1.33 
10. NiO 96 91 7.0 1.58 
11. Sm.sub.2 O.sub.3 
99 91 1.1 2.00 
12. Silica Gel 
97 97 1.7 2.50 
13. Cr.sub.2 O.sub.3 
99 95 2.7 1.58 
14. Bi.sub.2 O.sub.3 
99 96 2.1 2.50 
15. Y.sub.2 O.sub.3 
95 58 31.5 1.75 
______________________________________ 
##STR2## 
The hydroxypivaldehyde may be hydrogenated to neopentyl glycol using known 
chemical methods such as sodium borohydride reduction or catalytic 
techniques which involve conventional hydrogenation catalysts like copper 
chromite, nickel or alumina, or ruthenium on carbon. 
For example, an aldol reaction was performed using a stoichiometric amount 
of isobutyraldehyde and paraformaldehyde in the presence of 5 equivalent 
percent of triethylamine and 1 equivalent percent Nb.sub.2 O.sub.5. The 
stirred mixture was heated under an argon purge until a moderate 
isobutyraldehyde reflux was achieved. The reaction was terminated when 
isobutyraldehyde reflux ceased. The reaction solution was cooled to 
approximately 50.degree. C. and filtered to remove the Nb.sub.2 O.sub.5. 
The clear, faintly yellow filtrate was diluted to make a 15 wt. % solution 
in methanol and was then transferred into a 2 liter autoclave reactor. 
Copper chromite was added (3 wt. % based on aldol charge). Batch 
hydrogenation at 130.degree. C. for two hours at 3000 p.s.i.g. H.sub.2 
followed by a reduced pressure, 10-tray fractional distillation of the 
hydrogenation effluent gave neopentyl glycol product in .sup..about. 90% 
yield at &gt;99.5% purity.