78 Biological Chemistry. 



generally with substances containing several hydroxyl 

 groups. Its constitution is known from the fact that it 

 can be obtained by a series of reactions from tribrom- 

 propane of the formula CH 2 Br CHBr CH 2 Br. This bromine 

 derivative can be got from propylene, CH 2 : CH CH 3 , 

 which with bromine gives first propylene dibromide, 

 CH 2 Br CHBr CH 3 , from which by further action 

 of bromine in the presence of iron the compound 

 CH 2 BrCHBrCH 2 Br can be obtained. It is known that 

 the bromine atoms in this compound are all attached to 

 different carbon atoms, for if more than two were attached 

 to the same carbon atom, a substance having aldehydic or 

 ketonic properties would be obtained by the replacement 

 of the halogen by a hydroxyl group. 



One or more of the hydroxyl groups of glycerol can 

 be replaced by chlorine, giving rise to substances known 

 as the " chlorhydrins." 



Alcohols with a still larger number of hydroxyl groups 

 are known, of which may be mentioned erythritol, 



CH 3 (OH)CH(OH)CH(OH)CH 2 (OH), 



which is found native in certain lichens and sea-weeds, 

 and certain hexahydroxy alcohols, 



CH 2 (OH) - CH(OH)CH(OH)CH(OH)CH(OH) CH,(OH), 



of which mannitol (mannite), dulcitol (dulcite), and sor- 

 bitol (sorbite) occur native, and which are closely related 

 to the sugars (see p. 191 and seq.). 



OTHER ALCOHOLS. 



Alcohols are also known which may be considered as 

 derived from unsaturated hydrocarbons by the substitu- 

 tion of a hydrogen atom by a hydroxyl group. As an 

 example of substances of this character may be cited allyl 



