Method for catalytic rearrangement of 1,2-diglycerides into 1,3-diglycerides

A method is disclosed for the catalytic rearrangement of 1,2-diglycerides into 1,3-diglygerides by storage at raised temperature, in a solid state, until the ratio of 1,2- to 1,3-diglycerides is less than 1:4.

The present invention relates to a method for catalytic rearrangement of 
1,2-diglycerides into 1,3-diglycerides by storage at raised temperature, 
but in solid state, until the ratio of 1,2- to 1,3-diglycerides is less 
than 1:4. 
The rearrangement of 1,2-diglycerides into 1,3-diglycerides is described in 
British patent No. 1,369,438 and the equivalent Danish published 
application No. 132,886. Said patent describes a method in which mixtures 
containing 1,2-diglycerides are heated and kept in solid state for up to 7 
days so that the weight ratio of 1,2-diglycerides to 1,3-diglycerides 
becomes less than 1:6. 
According to the examples of said patent, most -- and perhaps all -- of the 
products in which the rearrangement occurs are prepared by the process 
described in Belgian patent No. 763,889 which is the equivalent of Danish 
patent No. 127,811. In said patent fatty acid esters of glycidol are 
treated with fatty acids while onium compounds, preferably quaternary 
ammonium compounds, catalyze the reaction. It can be difficult to 
completely remove these catalysts from the reaction product, and it is 
uncertain whether the permission of the health authorities can be obtained 
for using the products in nutrients and stimulants, as stated in Danish 
published patent application No. 132,882. 
It has now been found that the rearrangement proceeds only very slowly in 
the mixtures of partial glycerides prepared on a large technical scale by 
esterification of glycerol having less than 3 moles of fatty acids or by 
trans-esterification of triglycerides with glycerol. 
Said technical products are mixtures of mono-, di- and triglycerides, and 
the reactions for their preparation may be performed so that the ratio of 
the constituent components may be varied within very wide limits. 
Mixtures having maximum monoglyceride content are of specific importance. 
They consist of about 40% monoglyceride, about 50% diglyceride and about 
10% triglyceride. The diglycerides will most frequently consist of the 
equilibrium mixture having about 60% of 1,3-diglyceride and about 40% of 
1,2-diglyceride. The acids forming part of these glycerides are normally 
fatty acids having from 12 to 22 carbon atoms, especially stearic acid and 
palmitic acid. 
These technical glyceride mixtures are extensively used as emulsifying 
agents in the food and stimulant industries, and they also serve as 
starting materials for the preparation of monoglycerides by molecular 
distillation. Also these products are used in the food and stimulant 
industries. 
It has now surprisingly been found that the 1,2-diglycerides in mixtures of 
partial glycerides can be rearranged to 1,3-diglycerides by storage for a 
few days at raised temperature, but in solid state, when basic alkali 
metal compounds are used as catalysts. In accordance herewith the method 
according to the invention is specific in that during the rearrangement 
the mixture contains catalyst consisting of basic alkali metal compounds 
in amounts of at least 0.01% by weight calculated as sodium. 
The basic alkali metal compounds may, for instance, be alkali metal 
hydroxide or soap. Also alkali metal can be used, and a mixture of sodium 
and potassium with a melting point lower than 60.degree. C. is suitable. 
In principle, alkali metal alcoholates are applicable too, but this will 
result in the formation of the corresponding alcohol-fatty acid esters 
which may be difficult to remove from the reaction product. 
The rearrangement takes place at a temperature between room temperature 
(about 25.degree. C.) and the initial melting point of the glyceride 
mixture, preferably between 40.degree. C. and the initial melting point of 
the mixture. 
After the rearrangement the 1,3-diglycerides can be isolated by 
fractionation using hexane or acetone as solvent, and as side product 
there is obtained a fraction with higher monoglyceride content than the 
starting material, and said fraction can be used directly as emulsifying 
agent in the food and stimulant industries, or the fraction may be 
subjected to molecular distillation for the preparation of technical 
monoglycerides with a higher yield than obtained with the previously used 
starting materials. 
The formed 1,3-diglycerides can be esterified in a known manner with fatty 
acids for the preparation of desired triglycerides. Especially when 
esterifying 1,3-diglycerides containing stearic acid and palmitic acid 
with oleic acid, triglycerides of the same type as in cocoa butter are 
obtained.

The method according to the invention will be illustrated in greater detail 
by the following examples, of which examples 1 and 4 are comparative 
examples. It should be noted that the test to determine 1,2- and 
1,3-diglycerides gives the ratio between them with a relative uncertainty 
of 10%. All percentages in the examples are based on weight. 
EXAMPLE 1 
A commercial monoglyceride intended for use as emulsifying agent in the 
food industry was prepared by trans-esterification of fully hydrogenated 
soybean oil with glycerol. The sample contained 42% of monoglyceride and 
0.02% of soap, and the ratio of 1,2- to 1,3-diglycerides was 42:52. The 
powdered sample was stored at 46.degree. C., and after 4, 8 and 12 days' 
storage the ratio of 1,2- to 1,3-diglycerides was 40:60, 39:61 and 36:64, 
respectively. 
The rearrangement which has occurred is unimportant to the recovery of 
1,3-diglycerides. 
EXMAMPLE 2 
To a melted sample of the same type as used in Example 1 was added so much 
sodium hydroxide solution that the soap content was 0.8% corresponding to 
a sodium content of 0.062%, after which the sample was vacuum dried and 
made into powder. The ratio of 1,2- to 1,3-diglycerides was then 34:66. 
After storage at 46.degree. C. for 4 and 12 days the ratio of 1,2- to 
1,3-diglycerides was 19:81 and 4:96, respectively. 
EXAMPLE 3 
A sample of commercial monoglyceride containing 0.6% of soap corresponding 
to 0.046% sodium was stored at 46.degree. C. for 12 days. Thereby the 
ratio of 1,2- to 1,3-diglycerides decreased from 37:63 to 14:86. 
EXAMPLE 4 
A sample of the same type as used in Example 3 was washed with a small 
amount of citric acid solution, dried and filtered. This reduced the soap 
content to 0. By storage at 46.degree. C. for 15 days the ratio of 1,2- to 
1,3-diglycerides decreased from 44:58 to 39:51, that is without technical 
importance. 
EXAMPLE 5 
A sample of the same type as used in Example 3 was admixed with sodium 
hydroxide solution and vacuum dried. The sample then contained 1.8% of 
soap corresponding to 0.14% sodium. By storage at 46.degree. C. the ratio 
of 1,2- to 1,3-diglycerides decreased from 43:57 to 29:71 and 4:96 after 4 
and 12 days, respectively.