Process for the preparation of alkali metal salts of acyl cyanamides

The present invention is for a process for the preparation of alkali metal salts of acyl cyanamides, especially those of aliphatic carboxylic acids by reacting carboxylic acid esters of lower alcohols with monoalkali metal cyanamides. The reaction results in a process which is simple and efficient and one which can be used in commercial scale batch or continuous operations.

BACKGROUND OF THE INVENTION 
Acyl cyanamides in the form of their alkali salts have been known for a 
long time. The sodium salt of acetyl cyanamide was described as early at 
1878 (J. prakt. Chemie 17 9-11, 1878). The sodium salts of acyl cyanamides 
of long-chain fatty acids, resin acids or naphthenic acids and their 
application as soap-like tensides for detergents and wetting agents are 
known from the British patent specification No. 428,091 of the year 1935 
and also from the German patent specification No. 708,428 published in the 
year 1941. For the preparation of the short- as well as long-chain acyl 
cyanamides, the respective acid chlorides or acid anhydrides were first 
reacted with an excess of cyanamide to form the acyl cyanamide, which was 
then converted to the alkali metal salt in an additional step. A process 
for the preparation of bifunctional acyl cyanamides, for example adipic 
acid dicyanamide, by conversion of dicarboxylic acid chloride or 
dicarboxylic acid ester with cyanamide in alcoholic solution in the 
presence of substances which have an alkaline reaction and by refluxing is 
known from the German Offenlegungsschrifts Nos. 20 22 491 and 20 22 492. 
Similarly, a process for the preparation of sodium formyl cyanamide by 
conversion of ethyl formate with sodium cyanamide in alcoholic solution by 
refluxing is described in the German Offenlegungsschrift No. 27 57 586. 
Finally, substituted cyanoamines, which also include acyl cyanamides of 
C.sub.1 -C.sub.20 -carboxylic acids in their general formula, are said to 
be obtainable by conversion of the amines or amides with cyanogen bromide 
in benzene according to the European Offenlegungsschrift No. 8 475; the 
corresponding sodium salt is said to be obtained by dissolving in 
concentrated sodium hydroxide solution, reaction with ammonium carbonate 
and extraction with isopropyl alcohol. 
Although the acyl cyanamides of the long-chain fatty acids thus are 
soap-like tensides that have been known for almost 50 years, this type of 
compound has so far not been given any commercial attention as raw 
material for detergents. Not the least reason for this are the 
manufacturing conditions according to the known methods, which are 
unsuitable for large-scale production. These methods were difficult and 
time-consuming in the case of the fatty acid chlorides or fatty acid 
anhydrides as starting materials since the free acyl cyanamides are 
obtained initially and the preparation of the alkali metal salts requires 
an additional step. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide an improved process for 
the production of acyl cyanamides. 
It is another object of the present invention to provide a process for the 
production of acyl cyanamides derived from aliphatic carboxylic acids of 6 
to 30 carbon atoms. 
Another object of the present invention is to provide a simple and 
efficient method for the preparation of alkali metal salts of acyl 
cyanamides which is suitable for commercial scale batch or continuous 
operations. 
A further object of the present invention to react a monoalkali metal salt 
of cyanamide with a carboxylic acid ester of a lower alcohol at normal 
pressure and temperatures between 100.degree. to 300.degree. C. 
These and other objects of the present invention will become more apparent 
as the description thereof proceeds. 
DESCRIPTION OF THE INVENTION 
Now it was found that alkali metal salts of acyl cyanamides, particularly 
the acyl cyanamides of aliphatic carboxylic acids, can be prepared by 
reacting the respective carboxylic acid esters with monoalkali metal 
cycanamide by a process that also can be used with advantage on a 
commercial scale. The new manufacturing process is characterized by the 
fact that the carboxylate of a lower alcohol is mixed in eqimolar 
quantities with a solid, preferably anhydrous monoalkai metal salt of 
cyanamide and that this mixture is heated to a temperature between 
100.degree. and 300.degree. C. 
In principle, the process according to the invention does not require any 
solvent; and it was surprising to find that the reaction between ester and 
the alkali metal salt of the cyanamide takes place also without the 
presence of an alcoholic solvent. However, the process according to the 
invention requires higher initial temperatures than the reflux 
temperatures of the lower alcohols, i.e., temperatures above 100.degree. 
C. The lower by product alcohol set free during the formation of the acyl 
cyanamide collects in the reaction medium and can be removed from it under 
the proper pressure, by distillation. The esters of the lower alcohols 
methanol, ethanol or isopropanol are used preferably and the reaction is 
allowed to take place under normal pressure so that the alcohol is 
distilled off as it forms, and the amount of alcohol distilled off 
provides a measure for the continuation of the reaction. The reaction is 
completed when the alcohol ceases to form and distill off. In the process 
according to the invention, the formed, low-boiling alcohol may remain if 
the reaction is performed in a pressure vessel. However, the advantage of 
the easier agitation of the reaction mixture obtained in this case is more 
than offset by the disadvantage of having to work in a pressure vessel, 
which is a complex apparatus. On the other hand, if the ester of an 
alcohol boiling above the selected reaction temperature at normal pressure 
is used with the process according to the invention, the conversion can be 
carried out under reduced pressure, at which the formed alcohol distills 
over. 
For the sake of technological simplicity, the process according to the 
invention is carried out preferably at normal pressure and without the 
addition of a low-boiling alcohol as solvent. Under these conditions, the 
products of the process are obtained in solid form immediately after 
cooling, and the conversion of the product, which initially collects at 
the warm temperature as a viscous melt, into prills, needles, flakes, 
powder or other solid forms suitable for further processing is possible 
without difficulty. In contrast to the known processes considerably higher 
reaction temperature at which the forming alcohol distills over 
continually shortens the reaction time markedly. When the process permits 
it the operation without solvents may be performed, according to the 
invention, continuously. 
Among acyl cyanamides will be generally understood the carboxylic acid 
cyanamides themselves and those containing optional groups in the acyl 
radical. Therefore there can be prepared in accordance with the present 
invention acyl cyanamides from aliphatic, aromatic, alkyl aromatic and 
heterocyclic carboxylic acids. The acyl radicals can be substituted as 
needed, or they may contain heteroatomic bridge members such as an oxy or 
imino group, for example. The structure of the possible acyl radicals is 
limited only by the obvious requirement that the acyl radicals or their 
substutients and bridge members are inert under the reaction conditions. 
The term acyl cyanamides also includes the derivatives or di- or 
tricarboxylic acids or generally of polycarboxylic acids. 
The process according to the invention concerns above all, the preparation 
of the alkali metal salts of acyl cyanamides of aliphatic carboxylic 
acids, preferably of monocarboxylic acids and here particularly the 
preparation of the alkali metal salts of acyl cyanamides of long-chain 
aliphatic carboxylic acids with 6 to 30 carbon atoms in the acyl radical. 
The preparation of the alkali metal salts of acyl cyanamides of the 
C.sub.6 -C.sub.30 -fatty acids, especially of the C.sub.10 -C.sub.24 
-fatty acids, is a very particular objective of the invention. Of these, 
the fatty acid cyanamide alkali metal salts of the C.sub.12 -C.sub.18 
-fatty acids are most suitable as tensides for use in washing and cleaning 
agents. Fatty acid cyanamide alkali metal salts can now be prepared in 
very pure form and in large amounts by the process according to the 
invention. The invention made the alkali metal salts of the fatty acid 
cyanamides available as commercially important tenside raw materials on 
basis of fatty products. These have, in contrast to conventional soaps, 
lower susceptibility to hydrolysis. The alkali metal salts of the fatty 
acid cyanamides prepared according to the invention are therefore 
interesting intermediates for the formulation of new washing and cleaning 
agents. 
The carboxylic acid ester of a lower alcohol used as starting material is 
particularly the ester of a monovalent lower alkanol with 1 to 5 C-atoms; 
i.e., the methyl, ethyl, and propyl esters, also the butyl and pentyl 
esters are used as starting materials. But in principle, the carboxylic 
acid esters of lower di- and trihydric alcohols can also be used. Under 
certain conditions, the carboxylic acid ester of glycerin, also 
particularly the natural fats occurring in the form of triglycerides, are 
suitable as starting material. The fatty acid triglycerides can be used as 
carboxylic acid esters when the glycerin formed during the process does 
not interfere as a contaminent component of the desired product of the 
process in the subsequent commercial use of the latter, or when its 
presence is desirable. Consequently, the use of the fatty acid 
triglycerides as starting materials does not necessitate reaction 
conditions under which the formed glycerin is distilled off, although the 
removal by distillation through the choice of reaction temperatures and 
pressure ranges is basically possible. 
But the choice of carboxylic acid ester is generally determined by criteria 
such as ready commercial availability of the ester and simple performance 
of the process. Thus the fatty acid methyl esters are the carboxylic acid 
esters of choice for commercial batch processes. 
The solid cyanamide is used in the form of the mono-alkali metal salt of 
lithium, sodium or potassium as the second reaction component in the 
process according to the invention. The monosodium salt of cyanamide is 
used preferably mainly for its price. In the process, the dry, i.e. 
anhydrous, alkali metal salt of cyanmide is given preference when the 
absence of conventional soap as by-product is important. But the presence 
of the usual alkali metal soaps as by-products can be in many cases 
tolerable or even desirable for the subsequent further processing of the 
product of the process. 
The process according to the invention allows a variation of the reaction 
temperature within broad limits. The lower limit for the reaction 
temperature range essentially depends on the level of the initial 
temperature at which the two thoroughly mixed reaction components begin to 
react with each other, while the upper limit of the reaction temperature 
is practically detemined by the consideration and avoidance of undesirable 
side reactions, especially discolorations. A reaction temperature in the 
range from 100.degree. to 250.degree. C. proved to be suitable and 
preferable for commercial operations. When reaction temperatures in the 
range of 250.degree. C. or higher are chosen for the process, the problem 
of thermal decomposition can be avoided by staying within the process 
time, which is short under these conditions. 
The progress of the process can generally be measured by the alcohol 
formation; or by determining the amount of remaining ester e.g. by gas 
chromatography or as the portion insoluble in water. Infrared spectroscopy 
is well-suited for the determination of the reactants since all reactants 
have characteristic, strong absorption at different wave lengths, e.g.: 
NaHNCN: 2120 and 2170 cm.sup.-1 ; 
fatty acid esters: about 1750 cm.sup.-1 ; 
stearic acid cyanamide-Li: 2180, 1600 and 1390 cm.sup.-1 ; 
stearic acid cyanamide-Na: 2160, 1515 and 1390 cm.sup.-1 ; 
stearic acid cyanamide-K: 2160, 1560 and 1380 cm.sup.-1. 
The alkali metal salts of the fatty acid cyanamides are solid, colorless to 
slightly yellowish substances with a brittle to waxy consistency at room 
temperature. They soften at higher temperatures and melt above 100.degree. 
to 150.degree. C., depending on their composition, to form viscous 
liquids. The melting points are not characteristic. The technically 
especially interesting fatty acid esters of naturally occurring fatty 
acids are generally used as mixtures, i.e. as compounds with fatty acid 
radicals of varying lengths, and a sharp melting point consequently cannot 
be expected as a characteristic of the substance. 
The choice of equipment in which the process according to the invention can 
be carried out depends on the batch sizes and the rheological properties 
of the reaction mixture at the chosen reaction temperature. Acceptable 
are, e.g., conventional heated agitator tanks, kneading machines, but also 
tube reactors with attachments for the recovery of the free alcohol. After 
the reaction is completed, the products of the process can be conveyed 
directly as melts, e.g. through heated pipes, for further processing. 
According to another processing variation, the melts can be turned into a 
solid form suitable for storage or further processing by converting them 
into prills, needles or flakes. The preparation of an aqueous concentrate 
by dissolving in water is also possible, but the very fact that the alkali 
metal salts of the fatty acid cyanamides can be obtained directly in dry 
form is an advantage for many applications. It is well known that the most 
important commercial tensides of the sulfonate and sulfate type are used 
as aqueous paste concentrates for large-scale operations. However, the 
water content of these pastes frequently is considered a disadvantage, for 
example in the manufacture of detergent powders by hot spray-drying of an 
aqueous slurry in spray towers. In this important large-scale process for 
the preparation of detergents in powder form, it is an advantage when the 
active substances contain as little water as possible to keep the water 
content in the slurry. In this case the amounts of energy required for the 
removal of the water during the subsequent spray-drying is also low. 
Another aspect of the invention concerns the supply of the alkali metal 
salts of the acyl cyanamides in a form that does not have in the melt the 
generally high viscosity of the pure compounds and which is therefore 
easier to pump and agitate. This additional example of the invention is 
characterized by the addition of a high-boiling, water-soluble substance, 
which is inert under the reaction conditions, as a flux for the reaction 
components. Suitable as fluxes are mainly substances that do not interfere 
during the subsequent further processing of the product of the process by 
their presence; particularly suitable as additives are those substances 
the presence of which is expressly desired during further processing of 
the product. In the case of the further application of the products as 
tensides for the preparation of detergents and cleaning agents, the 
suitable flux additions are especially polymerization products with 
ethylene oxide and/or propylene oxide, e.g. polyethylene glycols, block 
polymers of ethylene oxide and propylene oxide, adducts of ethylene oxide 
and/or propylene oxide with long-chain alcohols, alkyl phenols or fatty 
acid amides. The nonionic tensides, which frequently are components of 
detergent and cleaning agent formulations, also belong to this group of 
compounds. The addition of a flux usually also results in a lowering of 
the initial temperature. In the broadest sense, the glycerin forming in 
situ, after the addition of fatty acid triglycerides as starting material, 
is also to be considered a flux. In this case, the process conditions with 
respect to temperature and pressure are chosen to keep the formed glycerin 
in the reaction medium. The alkali metal salts of the fatty acids, i.e. 
the conventional soaps, are also suitable as fluxes. Again, soap does not 
need to be added separately; rather, it is possible and also advantageous 
in this case to use an incompletely dried, i.e. still hydrous alkali metal 
cyanamide as a reactant, so that the soap is formed in situ as flux during 
the reaction. The essentially identical result can be obtained by the use 
of anhydrous alkali metal cyanamide together with alkali metal hydroxide. 
The following examples are given by way of explanation and not by way of 
limitation.

EXAMPLES 
EXAMPLE 1 
In a 1 liter three-neck flask with agitator, internal thermometer and 
attached distillation bridge, 253 g (1.5 mole) methyl ester of the first 
cut of coconut fatty acids (saponification number 332) containing mainly 
C.sub.6 -C.sub.12 fatty acids were well agitated with 96 g (1.5 mols) 
anhydrous monosodium cyanamide, and the mixture was heated to 155.degree. 
C. Most of the methanol formed distilled over within two hours, while the 
contents of the flask thickened but remained sufficiently fluid for 
agitation. The contents of the flask were poured out and congealed into a 
brittle, whitish solid that formed a clear solution in water. The infrared 
spectrum of the reaction product had characteristic absorptions at 2160, 
1515 and 1390 cm.sup.-1, which identified the product as the sodium salt 
of carboxylic acid cyanamide. 
EXAMPLE 2 
In the equipment described in Example 1, 270.5 g (1 mol) commercial grade 
isopropyl myristate and 64 g (1 mol) monosodium cyanamide were heated in 
the same manner to 170.degree. C. for 21/2 hours. The isopropyl alcohol 
formed during the reaction was almost completely distilled off after 2 
hours. The reaction product was obtained as highly viscous paste that 
could not be poured from the flask. The product congealed upon cooling 
into a brittle, whitish solid that produced a clear solution in water. The 
yield was quantitative. 
EXAMPLE 3 
In a 1 liter three-neck flask with agitator and thermometer, 289.2 g (0.33 
mol) of a technical grade triglyceride mixture of palmitic and stearic 
acid (hardened tallow) (saponification number 194) and 64 g (1 mol) 
monosodium cyanamide were heated to 160.degree. C. The contents of the 
flask thickened after only 15 minutes, but were easy to agitate. The 
reaction mixture was poured out after 30 minutes at 160.degree. C. and 
congealed upon cooling into a wax-like solid that produced a clear 
solution with water. Yield 345 g (97%). The infrared spectrum of the 
product showed the bands of glycerin in addition to the characteristic 
acyl cyanamide bands. 
EXAMPLE 4 
In a 500 ml three-neck flask with agitator, thermometer and attached 
distillation bridge, 100 g (0.42 mol) of a methyl ester of coconut fatty 
acid (saponification number 235) (chain length C.sub.12 -C.sub.18) and 27 
g (0.42 mol) anhydrous monosodium cyanamide were mixed and quickly heated 
to an internal temperature of 240.degree. C. with an oil bath preheated to 
260.degree. C. 
The formation of methanol began after 15 minutes and was completed after an 
additional period of ten minutes. The reaction mixture became viscous 
during this process. After a total time of 30 minutes, the infrared 
spectrum of a sample was recorded and the absence of ester absorption 
bands was established. The viscous product was poured out and congealed 
into a yellowish solid that dissolved readily in water. The product had 
the characteristic IR-spectrum of the sodium salts of fatty acid 
cyanamide. Yield 256 g (95%). 
EXAMPLE 5 
In the apparatus of Example 4, 143.7 g (0.5 mol) of the methyl ester of the 
hydrogenated tallow fatty acids acids (saponification number 195) and 40 g 
(0.5 mol) monopotassium cyanamide were mixed and heated to 160.degree. 
C.-170.degree. C. for 2 hours. Then, the viscous reaction product was 
poured out; it congealed upon cooling into a yellowish, water-soluble 
solid. The product was identified as acyl cyanamide potassioum salt by its 
infrared spectrum. Yield 154 g (92%). 
EXAMPLE 6 
In the apparatus described in Example 1, 230.4 g of the methyl ester of 
coconut fatty acids (saponification number 243.5), 64 g (1 mol) monosodium 
cyanamide and 50 g of the adduct of 10 mols ethylene oxide and tallow 
alcohol (trade name Eumulgin 010, registered trademark) were mixed and 
heated to 160.degree. C. The reaction was complete after 3 hours, when 
practically the total calculated amount of methanol had distilled over. 
After a total reaction time of 5 hours, the thin and easily agitated 
contents of the flask were poured out. After cooling, the reacton product 
was obtained as a wax-like white-yellowish, readily water-soluble mass. 
The product showed the typical bands of aliphatic ethers in addition to 
the characteristic bands of the sodium salt of fatty acid cyanamide. Yield 
289 g (93%). 
EXAMPLE 7 
In a batch that otherwise corresponded to that in Example 1, only 1.3 mols 
of the monosodium cyanamide instead of 1.5 mols of this salt were used 
together with 0.2 mol NaOH. The sodium soap formed besides the sodium acyl 
cyanamide during the reaction. The reaction mixture was easier to agitate 
and congealed upon pouring into a light-colored, wax-like solid. Its 
infrared spectrum showed the carbonyl bands of the soap at 1560 cm.sup.-1 
in addition to the bands of acyl cyanamide salt. 
EXAMPLE 8 
In analogy to Example 2, 298.5 g (1 mol) stearic acid methyl ester each 
were reacted in three different batches with 1 mol monolithium cyanamide 
(48 g) or 1 mol monosodium cyanamide (64 g) or 1 mol monopotassium 
cyanamide (80 g) at 150.degree.-170.degree. C. Reaction time 2-3 hours. 
The respective products--lithium salt of stearic acid cyanamide, sodium 
salt of stearic acid cyanamide, potassium salt of stearic acid 
cyanamide--were each obtained in quantitative yields in the form of 
slightly yellowish solids. 
EXAMPLE 9 
This example describes a continuous method of the process according to the 
invention. A suspension of 6.80 kg (106.3 mols) anhydrous monosodium 
cyanamide in 25.0 kg (106.3 mols) of a methyl ester of coconut fatty acids 
(C.sub.12 -C.sub.18) with the saponification number 238 was heated to 
60.degree. C. and was fed continuously into a screw reactor that was 
heated to 240.degree. C. The feeding rate was 0.6 liter/minute, which 
resulted in a mean reaction time of approximately 20 minutes for the given 
effective reactor volume of approximately 11 liters. The methanol, which 
escaped through the vapor outlets, was condensed in a descending glass 
cooler, while the formed sodium salt of the fatty acid cyanamide was 
transferred with the aid of an attached extruder to a flaking drum. 
The product congealed on the drum, which was cooled with tap water, and was 
obtained in the form of weakly-yellow-colored, completely water-soluble 
flakes. The infrared spectrum of the product showed the bands 
characteristic for sodium salts of fatty acid cyanamide at 2160, 1515 and 
1390 cm.sup.-1. The yield was 27.9 kg (98%); 3.1 kg methanol (91%) were 
also collected. 
The preceding specific embodiments are illustrative of the practice of the 
invention. It is to be understood, however, that other expedients known to 
those skilled in the art or disclosed herein, may be employed without 
departing from the spirit of the invention or the scope of the appended 
claims.