Violet

It is the simplest compound containing the -N = N- chromophore, but is of no practical importance since it lacks affinity for fibres. Normally it exists in the most stable trans form, but may be converted to a less stable, bright red as form, m.p. 71 -S C by ultra-violet irradiation. Cis to irans isomerization occurs rapidly on heating. 

BHC is manufactured by chlorination of benzene in the presence of ultra-violet light. The gamma-isomer is obtained from the crude mixture by selective crystallization, and forms colourless crystals, m.p. I13" C. U.S. production 1980 400 tonnes. 

CH3C(0)CH2Br. Colourless liquid which rapidly becomes violet in colour it is a powerful lachrymator b.p. 1367725 mm. Manufactured by treating aqueous propanone with bromine at 30-40 C it is usual to add sodium chlorate(V) to convert the hydro-bromic acid formed by the reaction back to bromine. It is not very stable and decomposes on standing. 

Chromium(IH) chloride, chromic chloride, CrClj. Violet solid (Cr plus CI2, hydrate plus SOCI2) only soluble in water in presence of Cr. Forms many complexes including the hydrates [Cr(H20)6]Cl3 - violet, [Cr(H20)jCl]Cl2,H20 - green, [Cr(H20)4Cl2]Cl,2H20 - green. 

The most common of the xanthophyll pigments, it is present in all green leaves, in blossoms and in various animal sources. It crystallizes in violet prisms with one molecule of methanol m.p. I93 C, soluble in organic solvents giving yellow solutions, li is related to a-carolene in the same way as zeaxanlhin is to /1-carolene. 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

Tiianium(III) chloride, TiClj. Violet or brown solid (TiCU plus H3 at 700°C TiCU plus AIR3 (brown form)). Forms violet 6 hydrate. Used as a reducing agent. The fibrous brown form is an active agent in the Ziegler-Natta siereoregular polymerization of olefines. 

Titanium JII) oxide, Ti203. Violet, formed by reducing TiOj with H2 at high temperatures. 

Tilanium IIf) sulphate, Ti2(S04)3,8H20. Formed as violet salt TiClj plus dil. H2SO4 with exclusion of O2. 

Vanadium ni) chloride, VCI3. Violet solid formed V plus HCl gas. VCIj bHiO formed from solution. Forms many complexes. 

Vanadium II) forms violet VS04,7H20 (electrolytic or Na/Hg reduction). Forms double salts. 

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