Process for preparing boric esters of glycerol fatty acid esters

Preparation of boric esters of glycerol fatty acid esters which comprises reacting triglycerides such as natural oils and fats with glycerol and boric acid in specific ratios. 3 mols of boric acid, 1 to 2 mols of at least one long-chain fatty acid triglyceride, and 4 to 5 mols of glycerol are interacted under neutral or acidic conditions at a temperature of 240.degree.-280.degree. C. According to the invention, boric esters can be obtained substantially in quantitative and good yield because of a small loss of reaction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a novel process for the preparation of boric 
esters of glycerol fatty acid esters. More particularly, it relates to a 
process for the preparation of boric esters of glycerol fatty acid esters 
which comprises reacting triglycerides such as natural oils and fats with 
glycerol and boric acid in specific ratios. 
2. Description of the Prior Art 
These materials are known as a substance having surface activity and are 
useful as an antistatic agent or emulsifier. 
Several processes of preparing boric esters of glycerol fatty acid esters 
are known including (1) a process in which glycerol and boric acid are 
heated for dehydration reaction to obtain a boric triester, and then the 
remaining hydroxyl groups of the triester are thermally dehydrated using 
fatty acids or are thermally dealcoholized using lower alcohol esters such 
as methyl esters of fatty acids thereby achieving the esterification of 
fatty acids, (2) a process in which fatty acid glycerol monoesters or 
mixtures thereof with glycerol are reacted and dehydrated with boric acid 
under heating conditions (Japanese Patent Publication Nos. 46-31847 and 
53-39413), and the like. 
However, these processes make use of fatty acids, lower alcohols of fatty 
acids, or fatty acid glycerol monoesters derived from oils and fats, thus 
requiring a number of very complicate steps. 
SUMMARY OF THE INVENTION 
We have made intensive studies to develop a process of more efficiently and 
more simply preparing boric esters of glycerol fatty acid esters. As a 
result, it was found that boric esters of glycerol fatty acid esters 
(hereinafter referred to simply as boric esters) could be directly 
produced from fatty acid triglycerides such as natural oils and fats. 
According to the present invention, there is provided a process for 
preparing a boric ester of a glycerol fatty acid ester which is 
characterized by interacting 3 mols of boric acid, 1 to 2 mols of at least 
one long-chain fatty acid triglyceride, and 4 to 5 mols of glycerol under 
neutral or acidic conditions at a temperature of 240.degree. to 
280.degree. C. 
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
In order to carry out the process of the invention, at least one long-chain 
triglyceride such as natural oils or fats, glycerol, and boric acid in the 
above-defined mixing ratios may be simultaneously charged and heated for 
reaction. Alternatively, glycerol and boric acid in the defined mixing 
ratio may be first esterified and dehydrated under heating conditions, to 
which long-chain fatty acid triglycerides such as oils and fats are added 
and heated for a subsequent reaction. The reaction is effected such that 
the reactants are sufficiently agitated at a temperature of 240.degree. to 
280.degree. C. for a period of about 1 to 10 hours, preferably 3 to 6 
hours, while heating and dehydrating, if necessary, in an atmosphere of an 
inert gas such as nitrogen gas. 
The long-chain triglycerides used as one of the starting materials of the 
invention are triesters of long-chain fatty acids and glycerol. Natural 
oils and fats or synthetic esters are used. The fatty acid moiety should 
preferably be saturated or unsaturated and have 8 to 22 carbon atoms. Most 
preferable examples of the triglycerides include animal oils such as beef 
tallow, lard and the like, and plant oils such as rape seed oil, cotton 
seed oil, soybean oil and the like. Especially, natural oils and fats 
containing residues of oleic acid and linoleic acid are preferable. 
The boric esters obtained according to the process of the invention are 
compounds of the following general formulas. In general, the boric esters 
are obtained in the form of mixtures of various compounds of the formulas. 
##STR1## 
in which X, Y, and Z independently represent an oH group or a 
##STR2## 
provided that at least one of X, Y, and Z is a 
##STR3## 
R is a saturated or unsaturated alkyl or alkenyl group having 7 to 23 
carbon atoms. 
As will become apparent from the above, it is not necessary according to 
the invention that fatty acid triglycerides such as natural oils and fats 
are converted such as by hydrolysis into fatty acids and lower alcohols 
esters of fatty acids, followed by reaction with boric acid. In other 
words, fatty acid triglycerides such as natural oils and fats can be 
directly reacted with glycerol and boric acid under limited conditions 
thereby quantitatively producing boric esters in high yield. 
In the process of the invention, it is unnecessary to remove low boiling 
alcohols such as methyl alcohol from the reaction system as in the known 
processes. The process of the invention has another advantage that the 
water produced by the reaction can be reduced by 25% over the known 
processes. The process of the invention is further advantageous in that a 
large number of starting materials are used, intended products can be 
obtained substantially in quantitative yield because of a small loss of 
reaction, and products can be directly obtained from inexpensive oils and 
fats by only one reaction step, thus the process being very efficient and 
economical. In addition, the process of the invention can also be applied 
to oils and fats having a number of unsaturated groups which are difficult 
in producing corresponding fatty acids.

The present invention is described by way of example. 
EXAMPLE 1 
20.1 g (0.32 mol) of boric acid was charged into a mixture of 97 g (0.11 
mol) of rape seed oil (IV: 120) and 50 g (0.54 mol) of glycerol, followed 
by reaction at a temperature of 255.degree. to 265.degree. C. for 5 hours 
in an atmosphere of nitrogen and removal of 17.5 g of the water produced 
by the reaction, thereby obtaining a product having an acid value of 133. 
The product was analysed with the result that it had a composition 
comprising a mixture of 50%, based on rough molar ratio, of boric esters 
of the general formulas (I) and (II) in which one of X, Y, and Z is an 
RCO.sub.2 group and the other two are independently hydroxyl group, about 
25% of boric esters of the formulas in which two of X, Y, and Z are 
independently an RCO.sub.2 group and the other is a hydroxyl group, about 
25% of boric esters of the formulas in which all X, Y, and Z are 
independently a hydroxyl group, and a small amount of boric esters of the 
formulas in which X, Y, and Z are all an RCO.sub.2 group. 
EXAMPLE 2 
24.1 g (0.39 mol) of boric acid was charged into a mixture of 116.4 g (0.13 
mol) of rape seed oil (IV: 77) and 60 g (0.65 mol) of glycerol, followed 
by reaction at a temperature of 255.degree. to 265.degree. C. for 5 hours 
in an atmosphere of nitrogen and removal of 23 g of the water produced by 
the reaction. As a result, there was obtained a product having an acid 
value of 129. 
The product was analysed with the result that it had a composition similar 
to that of Example 1 except for the type of long-chain alkyl group. 
EXAMPLE 3 
20.1 g (0.32 mol) of boric acid was charged into a mixture of 94 g (0.11 
mol) of cotton seed oil (IV:112) and 50 g (0.54 mol) of glycerol, followed 
by reaction at a temperature of 255.degree. to 265.degree. C. for 6 hours 
in an atmosphere of nitrogen and removal of 18 g of the water produced by 
the reaction. The resulting product had an acid value of 135. 
The product was analysed with the result that it had a composition similar 
to that of Example 1 except for the type of long-chain alkyl group. 
EXAMPLE 4 
20.1 g (0.32 mol) of boric acid was charged into a mixture of 93 g (0.11 
mol) of soybean oil (IV:120) and 50 g (0.54 mol) of glycerol, followed by 
reaction at a temperature of 255.degree. to 265.degree. C. for 6 hours in 
an atomosphere of nitrogen and removal of 16.3 g of the water produced by 
the reaction. The resulting product had an acid value of 129. 
The product was analysed with the result that it had a composition similar 
to that of Example 1 except for the type of long-chain alkyl group. 
EXAMPLE 5 
20.1 g (0.32 mol) of boric acid was charged into a mixture of 93 g (0.11 
mol) of lard (IV:66) and 50 g (0.54 mol) of glycerol, followed by reaction 
at a temperature of 260.degree. to 270.degree. C. for 4 hours in an 
atmosphere of nitrogen and removal of 19.2 g of the water produced by the 
reaction. The resulting product had an acid value of 125. 
The product was analysed with the result that it had a composition similar 
to that of Example 1 except for the type of long-chain alkyl group. 
EXAMPLE 6 
13.1 g (0.21 mol) of boric acid was charged into a mixture of 126 g (0.14 
mol) of rape seed oil (IV: 120) and 26 g (0.28 mol) of glycerol, followed 
by reaction at a temperature of 260.degree. to 270.degree. C. for 7 hours 
in an atmosphere of nitrogen and removal of 12 g of the water produced by 
the reaction. The resulting product had an acid value of 85. 
The product was analysed with the result that it had a composition 
comprising a mixture of about 50%, based on rough molar ratio, of boric 
esters of the general formulas (I) and (II) in which two of X, Y, and Z 
are independently an RCO.sub.2 group and the remaining one is 
independently a hydroxyl group, about 25% of boric esters of the formulas 
in which one of X, Y, and Z is an RCO.sub.2 group and the other two are 
independently a hydroxyl group, about 25% of boric esters of the formulas 
in which all X, Y, and Z are independently an RCO.sub.2 group, and a small 
amount of boric esters of the formulas in which X, Y, and Z are all a 
hydroxyl group. 
EXAMPLE 7 
35.3 g (0.57 mol) of boric acid was charged into a mixture of 90 g (0.19 
mol) of caprylic acid triglyceride and 87 g (0.95 mol) of glycerol, 
followed by reaction at a temperature of 250.degree. to 260.degree. C. for 
7 hours in an atomosphere of nitrogen and removal of 29 g of the water 
produced by the reaction. The resulting product had an acid value of 180. 
The product was analysed with the result that it had a composition similar 
to that of Example 1 except for the type of long-chain alkyl group.