THE CHEMISTRY OF PHOTOSYNTHESIS 273 



in nature was the discovery of Fischer and Passmore ^^ that formose con- 

 tains a-acrose, a synthetic sugar mixture, which Fischer and TafeP^ 

 showed to contain some of the naturally occurring sugars, i.e. the inactive 

 forms of glucose and fructose. From Nef's studies of the products ob- 

 tained by the action of alkalies on sugars he came to the conclusion that 

 formose consists of a mixture of half pentoses and half hexoses. Of the 

 hexoses there are 24 members present in the formose mixture, viz. 8 

 aldohexoses, 8 2-ketohexoses and 8 3-ketohexoses ; the aldoses constitut- 

 ing about one-half of the mixture are primarily dl-glucose and dl-galactose. 

 These definite statements of Nef will, however, require further sub- 

 stantiation. 



The mechanism of the condensation of formaldehyde to hexose and 

 pentose sugars has not yet been satisfactorily determined. Various the- 

 ories have been proposed ; these include : 



1. The intermediate formation of glycollic aldehyde, CHjOH . CH: O, 

 and the condensation of this to tetroses and hexoses. 



2. The intermediate formation of the trioses, glycerinealdehyde, 

 CHoOH . CHOH . CH : O, and dioxyaceton, CHoOH . C: O . CH2OH, 

 which then condense to hexoses. 



3. The stepwise condensation of one molecule of formaldehyde, with 

 the successive formation of diose, triose, tetrose, pentose, and hexose. 



The formation of glycollic aldehyde from formaldehyde has been re- 

 ported by H. and A. Euler ^^ by the action of calcium carbonate, though 

 Nef ^^ maintains that in the experiments of the former authors the calcium 

 carbonate must have contained some calcium hydroxide,*^ for Nef could 

 not obtain any sugar formation with either calcium carbonate or barium 

 carbonate even after heating the mixture for days. 



It is quite well established that glycollic aldehyde condenses to tetroses 

 and hexoses and Neuberg " reports the formation also of pentoses in this 

 condensation which implies a splitting of some kind. It is a question 

 therefore whether the pentoses are derived directly from formaldehyde or 

 through a degradation of the hexoses. 



Fischer ^^ regarded it as probable that glycerinealdehyde and dioxy- 

 acetone are intermediate products in the condensation of formaldehyde. 

 This was largely based upon the fact that a-acrose is obtained in this 

 manner and Fischer found some a-acrose in the formose mixture. H. and 



'•Fischer and Passmore, Ber. chem. Gcs., 22, 359 (1889). 



^Fischer and Tafel, ibid., 22, 97 (1889). Fischer, ibid., 23, 2114 (1890). 



"Euler, Ber. chem. Ges.. 39, 39, 43 (1906). 



"Nef, Ann. Chem., 403, 355 (1914). 



*'Pechmann, Ber. chem. Ges., 30, 2460 (1897). 



"Neuberg, Biochem. Zcit., 12, 339 (1908); Ber. chem. Ges., 35, 2630 (1902). 

 Fischer and Landsteiner, ibid., 25, 2553 (1892). Fischer, ibid., 27, 3200 (1894). 

 Nef, /. c, 205. 



"Fischer, Ber. chetn. Ges., 23, 2128 (1890). Piloty, ibid., 30, 3168 (1897). 

 Wohl and Neuberg, ibid., 33, 3108 (1900). 



