REDUCTION OF NITRATE AND NITRITE 53 



It was first shown by Thiele* that potassium nitrate, on 

 exposure to the rays from a quartz mercury vapour lamp, 

 was reduced to potassium nitrite with evolution of oxygen. 

 With a view to the further study of the photochemical de- 

 composition of nitrites, Baudisch f exposed mixtures of potas- 

 sium nitrite and methyl-alcohol in aqueous solution to diffused 

 daylight and to ultra-violet light and found that the methyl- 

 alcohol became oxidized to formaldehyde at the expense of 

 the nitrite which was reduced to hyponitrite, and this latter, 

 at its moment of formation, reacted with the formaldehyde 

 to produce the potassium salt of formhydroxamic acid (I.) 



KNO 3 + CH 3 OH = KNO + HCHO + H a O 

 KNO + HCHO = H . C . OH 

 II 



NOK 

 (I.) 



This reduction of nitrate or nitrite in presence of alcohol is 

 a purely photochemical reaction since no such change could 

 be produced in the dark even if the solutions were boiled. 



More recently Baly and his collaborators, to whose work on 

 carbohydrate synthesis reference has already been made, have 

 investigated the photosynthesis of nitrogen compounds from 

 nitrates and carbon dioxide by passing this gas through 

 aqueous solutions of potassium nitrate or nitrite exposed to 

 ultra-violet light. In these circumstances activated formalde- 

 hyde is produced for which the formula H . C . OH is suggested, 

 the activity being due to the divalent carbon. According to 

 Baly, Heilbron and Hudson J this activated formaldehyde 

 reacts with the nitrite to produce the potassium salt of 

 formhydroxamic acid (I.), an atom of oxygen being evolved 

 which oxidizes a further quantity of formaldehyde to formic 

 acid. These changes may be represented by the following 

 equations : 



H . C . OH + O : NOK -> H . C . OH -> H . C . OH 



II II + o 



0:NOK NOK 



and O + H . C . OH = HCOOH 



* Thiele: " Ber. deut. chem. Gesells.," 1907, 40, 4914. See also Moore 

 and Webster : " Proc. Roy. Soc.," Lond., B., 1919, 90, 158. 



f Baudisch: "Ber. deut. chem. Gesells.," 1911, 44, 1009. See also loc. 

 cit., 1916, 49, 1176, and 1918, 51, 793. 



, Heilbron and Hudson : " Journ. Chem. Soc.," 1922, 121, 1078, 



