ALDEHYDES 57 



formaldehyde are probably connected together through oxygen 

 atoms as under : 



CH 2 CH, 



O O and O O 



\ / / \ 



CH 2 CH 2 O CH 2 



Paraformaldehyde Trioxymethylene or 



Metaformaldehyde 



which accounts for the fact that they are readily broken up 

 into the simple molecules of formaldehyde by heating. 



II. A different type of polymerization, involving the link- 

 ing together of molecules of formaldehyde through carbon, is 

 also known ; this type of polymerization, which is sometimes 

 known as aldol condensation, results in the formation of a 

 more stable complex which cannot be reconverted into the 

 simple substance. 



The reaction takes its name from the substance produced 

 by the action of dilute hydrochloric acid or zinc chloride on 

 acetic aldehyde. 



CH 3 CHO + CH 3 CHO = CH 3 CHOH.CH 2 .CHO 



Aldol 



The analogous reaction with formaldehyde is, however, brought 

 about by dilute alkalis ; in this way two molecules of formal- 

 dehyde give rise to glycollic aldehyde, 



HCHO + HCHO = CH 2 OH.CHO 



Glycollic aldehyde 



or three molecules may combine together to produce glyceric 

 aldehyde, 



HCHO + HCHO + HCHO = CH 2 OH.CHOH.CHO 



Glyceric aldehyde 



By repeatedly shaking a 4 per cent solution of formal- 

 dehyde for half an hour with an excess of lime water, and then 

 filtering the solution and setting it aside for some days until 

 the odour of formaldehyde had disappeared, Loew * was able 

 to obtain a crude mixture of sugars called formose, from which 

 true reducing hexose sugars have been isolated. This change 

 may be represented by the equation : 



6HCHO = C 6 H 12 O 6 



* Loew : " Ber. deut. chem. Gesells.," 1887, 20, 142, 3039; 1888, 21, 

 270; 1889, 22, 470, 878. 



