Process for the preparation in a single stage of saturated omega-aminoacids from olefinically unsaturated omega-aldehydoacids

The specification describes a process for preparing saturated omega-aminods from olefinically unsaturated omega-aldehydoacids. According to the invention, the starting aldehydoacid is transformed into the corresponding iminoacid, and this is subjected to the hydrogenation both of the imino function and of the ethylenic double bond or double bonds, in a single stage and in the presence of an hydrogenation catalyst. The catalyst is a transition metal of one of the first two sub-groups of the VIII group of the periodic system, viz. is chosen among Fe, Ru, Os, Co, Rh, and Ir, and is used in the metal state or as a compound.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for transforming, in a single stage, 
olefinically unsaturated omega-aldehydoacids into saturated 
omega-amino-acids. The industrial importance of these useful products is 
well known and requires no demonstration. It suffices to recall, for 
instance, the very widespread use of these aminoacids as monomers for the 
manufacture of polyamides employed as plastic materials or in the textile 
field, for the production of "nylon" fibers and yarns. 
2. Description of the Prior Art 
These omega-aminoacids are defined by the general formula H.sub.2 
N--(CH.sub.2 --).sub.n+1 COOH wherein "n" is a whole number in the range 
from 4 to 16, and more commonly from 4 to 10. 
The olefinically unsaturated omega-aldehydoacids have been disclosed by the 
publication of patent applications No. 74 24188 in France and Pat. No. P 
24 33408 in the German Federal Republic by the applicant of this 
application. In said publications the methodology for obtaining such 
unsaturated aldehydoacids starting from cycloolefins comprising more than 
one ethylenic unsaturation, has also been described. Several 
omega-formyl-alkenoic acids, such as 11-formyl-4,8-undecadienoic acid, 
7-formyl-4-heptenoic acid, 9-formyl-4-nonenoic acid and 
9-formyl-6-nonenoic acid, with the respective production methodologies, 
had been described in the aforesaid publications. 
In a more general form, the linear unsaturated aldehydoacids which can be 
used according to the present invention to obtain the desired saturated 
omega-aminoacids, may contain from 1 to 3 olefinic double bonds and 
correspond therefore to the general formula 
EQU O.dbd.CH--(CH.sub.2 --).sub.60 (CH.dbd.CH--).sub.92 (CH.sub.2 --).sub.62 
(CH.dbd.CH--).sub.94 (CH.sub.2 --).sub.65 . . . (CH.dbd.CH--).sub.96 
(CH.sub.2 --).sub.67 COOH (I) 
wherein 
.alpha.,.beta., .gamma., .delta. = whole numbers, equal or different from 
one another, chosen among 0,1,2 and 3; 
.rho., .sigma., .tau. = whole numbers, equal or different from one another, 
chosen among 0 and 1; 
Provided that the following conditions are observed: 
EQU the sum .rho. + .sigma. + .tau. = 1,2 or 3; 
EQU the sum .alpha. + .beta. + .gamma. + .delta. + .rho. + .sigma. + .tau. = n 
(Examples: 7-formyl-4-heptenoic acid wherein .alpha. = 2, .beta. = 2, 
.gamma.= O, .delta. = 0, .rho. = 1, .sigma. = 0, n = 6; 
11-formyl-4,8-undecadienoic acid, wherein .alpha. = 2, .beta. = 2, .gamma. 
= 2, .delta. = 0, .rho. = 1, .tau. = 0, n = 10.) 
In the aforesaid patent publications the use of these unsaturated 
omega-aldehydoacids to obtain saturated omega-aminoacids had been 
contemplated. The methodology set forth in said publications for obtaining 
this result comprises a plurality of phases including two hydrogenation 
stages which are successive and clearly distinguished from one another. 
The first of said stages consists in the reductive amination of an 
unsaturated .omega.-aldehydoacid to the corresponding unsaturated 
.omega.-aminoacid, characterized by the fact that the unsaturated 
.omega.-aldehydoacid is transformed by means of ammonia and an alkali 
metal hydroxide in aqueous solution, into the salt of the corresponding 
unsaturated iminoacid, which latter is hydrogenated in the presence of a 
catalyst under conditions which lead to the hydrogenation of the imino 
group. The second of these stages consists in the hydrogenation of the 
unsaturated .omega.-aminoacid thus obtained to the corresponding saturated 
aminoacid, characterized by the fact that the alkali salt of the 
unsaturated aminoacid is reacted with hydrogen in the presence of a second 
catalyst, in order to hydrogenate the olenifinc double bonds. 
According to this previous methodology the hydrogenation catalyst of the 
first hydrogenation stage is preferably nickel, in the form of the metal 
or of salts thereof, pure or supported, or Raney nickel, whereas the 
second stage hydrogenation catalyst is preferably palladium in supported 
form. It had not been foreseen, nor was it in fact foreseeable in the 
light of the previous technical knowledge, that the two distinct 
hydrogenation stages could be conveniently substituted by a single stage 
using a single hydrogenation catalyst. Actually, if the catalyst employed 
for the hydrogenation of the imino groups were used under conditions 
(temperature above 150.degree. C) such as concurrently to catalyze the 
hydrogenation of the olefinic double bonds as well, one would obtain, 
beside the saturated .omega.-aminoacid, large quantities of undesired 
by-products, such as e.g. the corresponding secondary aminoacids, which 
are very harmful to the transformation of the .omega.-aminoacid to the 
corresponding polyamide as they would cause a cross-linking of the 
polyamide and the consequent lack of fusibility of the product. Likewise, 
if the catalyst for the hydrogenation of the olefinic double bonds 
(palladium) were concurrently used for the hydrogenation of the imino 
groups as well, one would equally obtain large amounts of secondary 
aminoacids as by-products, beside the .omega.-aminoacids. 
SUMMARY OF THE INVENTION 
It is now a purpose of the present invention to produce linear saturated 
omega-aminoacids, corresponding to the general formula 
EQU H.sub.2 N--(CH.sub.2 --).sub.n+1 COOH (II) 
wherein "n"is a whole number in the range from 4 to 16, and in general from 
4 to 10. In view of the substantially identical behaviour of the various 
compounds, it is held that it is sufficient that examples be given of the 
production of omega-aminoacids according to the above defined general 
formula, wherein "n"is 6 and 10. 
The process according to the present invention is characterized essentially 
by the fact that the said production is effected through a single stage 
hydrogenation, starting from unsaturated aldehydoacids comprising from 1 
to 3 olefinic double bonds, and corresponding to the general formula (I) 
hereinbefore set forth, to obtain, with yields above 80%, corresponding 
saturated aminoacids as defined by the said general formula (II). 
According to the invention, an .omega.-aldehydoacid according to the 
general formula (I) is transformed into the corresponding iminoacid, and 
this is subjected to the hydrogenation both of the imino function and of 
the ethylenic double bond or double bonds, in a single stage and in the 
presence of an hydrogenation catalyst consisting of a transition metal of 
one of the first two sub-groups of the VIII group of the elements' 
periodic system, viz. chosen among Fe, Ru, Os, Co, Rh, and Ir, preferably 
ruthenium or rhodium. 
In practice the iminoacid is obtained as an alkali salt by treatment with 
ammonia and an alkali metal hydroxide in aqueous solution, according to 
reaction diagram (III) set forth hereinafter, and is hydrogenated without 
isolating it, according to reaction (IV). Reactions (III) and (IV) may be 
carried out in a single stage, by reacting the aldehydoacid concurrently 
with ammonia, alkali hydroxide and hydrogen in the presence of the 
catalyst, or the alkali salt of the iminoacid, or a part thereof, may be 
firstly formed according to reaction (III) and the hydrogenation may be 
carried out thereafter in a single stage, whereby in any case there is 
obtained the alkali salt of the desired saturated aminoacid, from which 
the acid is obtained by treatment with an acid compound, according to 
known methods (V). 
##STR1## 
wherein M = an alkali metal; 
H'= an hydrogen atom of an acid compound; 
A = the residue of an acid compound; 
.alpha., .beta., .gamma., .sigma., .tau., .iota., .tau., n have the 
meanings specified hereinbefore. 
The metal chosen as the hydrogenation catalyst may be used in the metal 
state or as a compound, pure or preferably supported on a support such as 
activated charcoal, calcium carbonate, aluminium, silica, or 
silica-alumina. 
The hydrogenation temperature is from 70.degree. to 150.degree. C, 
preferably from 100.degree. to 140.degree. C. 
The aqueous solution of the alkali salt of the iminoacid which forms when 
aldehydoacid, ammonia and alkali metal hydroxide are mixed, should have an 
ammonia concentration from 10% to 50% (preferably from 20% to 30%) by 
weight of NH.sub.3 per weight of overall solution, to avoid the formation 
of secondary products, on the one hand, or a lowering of the solubility of 
the salt, on the other. 
Preferably but not necessarily the conditions are also observed that 
the hydrogen pressure for the hydrogenation is from 2 to 60 atmospheres: 
the duration of the hydrogenation is from 1 to 8 hours. 
One of the main advantages obtained through the use of the process 
according to the invention, is that the whole sequence of all the 
reactions illustrated in the general reaction diagrams (III), (IV) and (V) 
occurs with yields of saturated .omega.-aminoacid, referred to the initial 
.omega.-aldehydoacid, of at least 80% of the theoretical value. 
Other important advantages, with respect to the process disclosed in the 
above mentioned patent publications, are the following: 
1. Yield of at least 80% of saturated .omega.-aminoacid, while the 
previously known (single stage) techniques did not go over 70%. Therefore 
the losses of the starting .omega.-aldehydoacid are limited. Said yields 
are close to those which are attained by the previously known two stage 
process. 
2. The high yield facilitates the successive purification process, inasmuch 
as the by-products which are present are very few. 
3. Simplicity of the process, which is carried out in a single stage, 
whereas the previously known methods involved two hydrogenation autoclaves 
and the filtration of the catalyst between the first and the second stage. 
Therefore investment and operation costs are lower.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A number of preferred but not exclusive embodiments will be set forth 
hereinafter, together with a number of comparative examples, for the 
purpose of better demonstrating the progress afforded by the invention to 
the state of the art. 
EXAMPLE 1 
50 g. of ruthenium at 5% on charcoal (having a moisture content of50%), 220 
g. of a 32% by weight aqueous ammonia and hydrogen in the amount required 
to reach an overall pressure of 20 atm., are charged into a stainless 
steel autoclave having a volume of 2.7 liters, provided with a fast 
stirrer, a temperature control system and a dosing volumetric pump. 
Stirring is begun and concurrently the autoclave is heated up to 
130.degree. C. At this temperature the pressure becomes stabilized at 30 
atmospheres. 
In 16'there are fed into the autoclave, through the volumetric pump, 787 g. 
of an aqueous ammonia containing solution having the following 
composition: 92% 11-formyl-4,8-undecadienoic acid: 150.5 g.; aqueous (32% 
by weight) ammonia: 525 g.; aqueous (24.9% by weight) sodium hydroxide: 
101.8 g.; water: 10 g. 
While the imine solution is being fed into the autoclave, the temperature 
is maintained at 130.degree.-132.degree. C; the pressure is maintained at 
30 atmospheres by feeding hydrogen. At the end of the pumping of the imine 
solution, the reaction is continued for another 140'and then the solution 
contained in the autoclave is discharged through a filter and is 
concentrated so as to evaporate all the excess ammonia. 
The aqueous solution of the sodium salt of the aminoacid is purified by 
extraction with toluene. From the toluene solution small amounts of 
dodecamethylene-diamine are obtained. From the aqueous solution, by 
treatment with carbon dioxide at room pressure and at a temperature of 
98.degree. C, 12-amminododecanoic acid is obtained as a crystalline 
precipitate. The yield is 116.5 g. (82.5% of theory referred to the 
aldehyde groups of the initial formylundecadienoic acid). 
EXAMPLES 2 and 3 (comparative) 
In order to illustrate the advantages attained through the use of the 
catalysts herein described and claimed, in a comparison with catalysts 
consisting of other transition metals of the eighth group of the 
elements'periodic system, the results obtained with these latter in the 
amino-hydrogenation reaction of 11-formyl-4,8-undecanoic acid are set 
forth hereinafter. The hydrogenation conditions are the same as used in 
Example 1. 
______________________________________ 
Example Yield of 12-aminodo 
N.degree. 
Catalyst decanoic acid % 
______________________________________ 
2 5% Pt on charcoal 
20.5 
3 5% Pd on charcoal 
49.8 
______________________________________ 
The yield is referred to the aldehyde groups of the initial 
11-formyl-4,8-undecadienoic acid. 
EXAMPLE 4 (comparative) 
With the same purposes as in Examples 2 and 3, a comparison is made of the 
behaviour of finely divided nickel as a catalyst for the hydrogenation 
both of the imino groups and of the olefinic double bonds. The 
ydrogenation of the first is effected under the conditions described in 
Example 1, whereas for the hydrogenation of the olefinic double bonds the 
use of a temperature of 170.degree. C is required. The starting material 
and the other conditions are the same as used in Example 1. 
After purification, 12-aminoundecanoic acid is obtained with a yield of 60% 
referred to the aldehyde groups of the starting material. 
EXAMPLE 5 
Example 1 is repeated using 7-formyl-4-heptenoic acid (148 g.) as a 
starting material to be subjected to the amino-hydrogenation. The catalyst 
employed is ruthenium metal (55 g. at 5%, supported on charcoal) which is 
loaded into the autoclave as described in Example 1. The reaction is 
carried out at 135.degree. C and at 40 atmospheres and the absorption of 
hydrogen lasts 180'after the end of the pumping of the ammonia containing 
solution of the unsaturated aldehydoacid. At the end of the reaction, 
after filtering the catalyst, the excess ammonia is evaporated, the 
solution is concentrated to a small volume and it is acidified with a weak 
acid. Upon the addition of alcohol, 8-amino-octanoic acid, m.p. 
188.degree.-190.degree. C, is separated (yield 85%). 
EXAMPLE 6 
Example 1 is repeated using rhodium metal as the catalyst. 20 g. of 5% 
rhodium (supported on charcoal) and 150 g. of concentrated ammonia are 
charged into the autoclave having a volume of 2.7 liters described in 
Example 1. The temperature of the autoclave is brought to 13.degree. C, 
the pressure is brought to 30 atmospheres by means of hydrogen, and an 
ammonia containing aqueous solution of 11-formyl-4,8-undecadienoic acid in 
the amount and with the composition set forth in Example 1 is pumped into 
the autoclave. After the introduction of the aldehydoacid has ended, the 
temperature is brought to 135.degree.-138.degree. C and the pressure to 45 
atmospheres. The absorption of hydrogen continues for 300 more minutes, 
then the pressure is discharged from the autoclave, the catalyst is 
filtered and the 12-aminododecanoic acid is separated from the solution as 
described in Example 1. (Yield 120 g. = 84.5% referred to the aldehyde 
groups of the formylundecanoic acid employed). 
The examples which have been described have only an illustrative value, as 
the invention may be carried into practice in many other ways, without 
departing from the scope of this patent.