THE MECHANISM OF ORGANIC SYNTHESIS 121 



It will be seen that although water must enter into reaction there i 

 addition of water to the aldol in order to form the butyric acid. 



It has been suggested that similar reactions might account for the forma 

 tion of the higher fatty acids, in which case one molecule of acetic aldehyde 

 would be added to the fatty acid in order to build up the acid which is i.'.-xt 

 highest in the series. Although certain of the higher acids have been ),- 

 pared in this way, proof is still wanting that a continuous series of 

 theses may be effected by the continuous addition of aldehyde. Such a 

 hypothesis is, however, more probable than the direct conversion of three 

 molecules of sugar into one molecule of stearic acid. The latter change 

 would be associated with a very great absorption of energy, whereas a con- 

 tinuous building up of fatty acids by the addition of aldehyde obtained 

 through lactic acid from the disintegration of hexose molecules only requires 

 a small expenditure of energy, which could be obtained by the combustion 

 of the formic acid formed as a by-product in the process. If we suppose that 

 the synthesis of the higher fatty acids from sugar is carried out in this way, 

 the energy equations would be as follows (Leathes) : 



1 g. mol. glucose ) > (2 g. mols. aldehyde + 2 g. mols. formic acid. 



677-2 cals. / \ 2 x 275-5 + 2 x 61-7 



= 674-4 cals. 



2 g. mols. aldehyde j , /I g. mol. aldol \ fig. mol. butyric acid. 



551 cals. / *~\ 546-8 cals. / *"\ 517-8 cals. 



Or, tracing the same change on as far as palmitic acid: 



4 g. mols. glucose ^ f 1 g. mol. palmitic acid + 8 g. mols. formic acid. 



2708 cals. f~\ 2362 cals. + 494 cals. 



- 2856 cals. 



In the first stage of the synthesis, the reaction leading to butyric acid, the 

 net result would be, supposing the formic acid to be oxidised, that some 160 

 calories, or nearly 25 per cent, of the whole energy, would be rendered avail- 

 able for other purposes. In the latter stages leading to palmitic acid some 

 of the energy derived from the oxidation of the formic acid would be required 

 for effecting the synthesis, and only about 12-5 per cent, of the original 

 amount contained in the sugar would be set free. It is worth noting that 

 in the butyric fermentation of sugar by micro-organisms there is a production 

 first of lactic acid, and this substance then disappears to give place to butyric 

 acid. At the same time carbonic acid and hydrogen are evolved, both gases 

 being derived from the decomposition of the formic acid. In the process a 

 certain amount of caproic acid is always produced, and the crude butyric 

 acid of fermentation is used as the source from which commercial caproic 

 acid is derived. 



Attempts to produce the higher fatty acids by the condensation of success 

 molecules of aldehyde have so far only resulted in the production of branched 

 of carbon atoms, whereas the normal fatty acids of the body are straight chau 

 Raper has shown that the normal caproic acid may be formed by t 

 of aldol with itself. Miss Smedley has suggested that a more proba We 

 lies through pyruvic acid. Pyruvic acid, which may be produced in tl 



