# Ester of glycerol and glyceric acid

What is the ester of glycerol ($$\ce{C3H8O3}$$) and glyceric acid ($$\ce{C3H6O4}$$)? I couldn't find any information about it online, so is this reaction even possible? I'm not sure what would happen, from my understanding, the alkyl of the alcohol replaces the hydrogen in ($$\ce{-COOH}$$) the carboxylic acid. But I can't work out this one.

I think it could be $$\ce{C6H12O6}$$ (mono ester) or $$\ce{C12H23O15}$$ (tri ester) , but I'm not sure. Is this correct? Is there a characteristic difference between the 3(mono, di or tri esters)? What dictates which one will be formed? Also, do the compounds have any significance?

• Since glycerol has 3 hydroxyl groups, you could have mono, di or tri-esters. How could it be C5? For a monoester it would be C3 + C3 = C6! – user55119 Mar 20 '19 at 22:07
• Oops! Missed that, could it be C12H23O15 (tri ester)? – Siddharth Khare Mar 20 '19 at 22:11
• There isn't enough information to make a decision. The triester will be C12 but if you use racemic glyceric acid there would be several diastereomeric triesters. PS: Can't have an odd number of hydrogens and the oxygens are wrong. Do you know what an ester is and the structures of the 2 reactants? – user55119 Mar 20 '19 at 22:19
• And don't forget, glyceric acid and react each other when its $\ce{COOH}$ is activated, depend on the method you'd use. – Mathew Mahindaratne Mar 20 '19 at 22:25
• That issue is readily averted by using the acetonide of glyceric acid for the esterification with glycerol. The acetonide can be hydrolyzed without affecting the ester. @Mathew Mahindaratne – user55119 Mar 20 '19 at 23:01

The formation of the triester of glyceric acid and glycerol cannot be done directly because of the poly-esterification of glyceric acid itself. This problem can be circumvented by employing the acetonide of glyceric acid. Subsequent to the esterification, selective hydrolysis of the acetonide in the presence of the esters can be effected.
Esterification with a single enantiomer of the acid would produce a single triester, either 1A or 1B. Esterification with the racemic acid could form, in principle, 16 (24) stereoisomers. However, this number is reduced to eight. Column A lists 6 permutations of the stereochemistry with two missing owing to the non-stereogenic nature of C2 in 1A and 4A. Column B lists the enantiomers of column A. Rows 2 and 5 are duplicate as are rows 3 and 6. The eight stereoisomers are within the black box (1A through 4B). While the enantiomeric pairs in each row (1, 2, 3, 4) are formed in equal amounts, the four racemates are not necessarily formed in equal amounts.
The assignment of the r/s descriptors at pseudoasymmetric center C2 in stereoisomers 2A, 2B, 3A and 3B are governed by the 2013 CIP Rules 1a and 5.