REACTIONS OF THE QUINONES 435 



Detection and Determination 



Only brief mention of the various ways in which quinones can be deter- 

 mined will be made, since the methods are well described in the standard 

 works on organic analysis. The 1,4-quinones have rather intense absorption 

 bands around 240-245 m//, which are shifted to somewhat longer wave- 

 lengths by alkylation, and reduction to the hydroquinones brings about 

 marked changes in the absorption, with new peaks appearing around 

 290-295 m//. Ultraviolet absorption measurements may be of use for char- 

 acterizing the state of oxidation in a system or determining the purity of 

 samples, but are not of much use for quantitative determination of the 

 quinones in complex mixtures. The quinones may be treated in various 

 ways preparatory to spectro photometric determination. For example, 1,4- 

 naphthoquinone may be determined at 583 mju following reaction with 

 malononitrile, this detecting concentrations as low as 0.003 mM (Gonter 

 and Petty, 1963). Menadione may be analyzed in biological material by 

 reacting with 2,4-dinitrophenylhydrazine with determination of the ab- 

 sorbance at 635 m//, this being useful in the range 2-300 //g (Sathe et al., 

 1957). 



Polarographic methods are frequently applicable to quinones. Half- 

 wave potentials for many quinones are given by Kolthoff and Lingane 

 (1952, p. 699), and a chapter is devoted to quinones in the book by Brezina 

 and Zuman (1958, Chapt. XIV, p. 185). Colorimetric methods are well 

 covered in a chapter on the quinones in the book by Snell and Snell (1953). 

 Many spot tests have been devised for the quinones and hydroquinones 

 — e. g., with Liebermann's reagent, phloroglucinol, or o-phthalaldehyde — 

 and vary greatly in sensitivity and specificity (Feigl, 1960). Most spot tests 

 can detect 1-10 //g of a hydroquinone. Paper chromatography was used 

 by Sproston and Bassett (1954) for the detection and determination of 

 various substituted naphthoquinones, and the Rf values for these and some 

 benzoquinones are tabulated. In certain systems, hydroquinones may be 

 easily determined by reduction of Fe+++ and reaction of Fe++ with o- 

 phenanthroline to form the red complex; this method was used by Wo- 

 silait and Nason (1954) in their enzyme studies, 



REACTIONS OF THE QUINONES 



The tanning of skin by quinones and the concurrent physical changes 

 in the proteins stimulated extensive studies many years ago on the reactions 

 of the quinones with proteins, characteristic protein groups, and amino 

 acids. Additional impetus was supplied by the organic chemists who used 

 the quinones and hydroquinones extensively in synthetic procedures. The 

 primary points of attack on the proteins are presumably the SH and the 

 amino groups. 



