Io6 PLANT RESPIRATION 



(I) P(CoH5)3 + O, = PO,(C>H5)3 



(II) P02(C2H5)3 + CeHK >CH— HC< }C,n, = 



.COv /CO. 



PO(C.>H5)3 + H.>0 + CeH/ >C = C< >C6H4 



or 



(I) CeHs— CHO + O. = CeHs— CH< >0 



.Ox / CO^ 



(II) CeHs— CH< >0 + CbH/ >CH— 



^O^ ^NH^ 



/COv 

 HC< >C6H4 = C6H5— COOH + H2O + 



/COs^ _ /CO^^ 



C6H4\ /C C\ yCe,xli. 



Substances which are not oxidised by molecular oxygen but 

 by the oxygen of the moloxides, Engler called acceptors. In 

 the case before us, indigo white plays the role of the acceptor 

 and is oxidised to indigo blue by the oxygen of the moloxides. 

 In the absence of indigo white the surplus of triethyl phosphine 

 or of benzaldehyde would act as the acceptor, since the moloxides 

 are unstable and have to give up an atom of oxygen in some 

 way. The autoxidation of pure triethyl phosphine consists of 

 the following stages: 



(I) P(CoH5)3 + 0.> = PO.,fC.H5)3 



(II) POo(C2H5)3+ P(C.>H5)3 = 2PO(CoH5)3; 



and combined, 



2P(CoH5)3 + Oo = 2PO(CoH5)3. 



The autoxidation of benzaldehyde is accomplished in a 

 similar way: 



(I) CeHs— CHO + O2 - CeHa— CH< >0 



^0^ 



