LII.—The progressive bromination of toluene

A Simple, Safe and Efficient Synthesis of Tyrian Purple (6,6′-Dibromoindigo)

“…This was filtered off, washed with 2 × 20 mL H 2 O, and dried in vacuo to give of the desired product (3.35 g) softening at 145 ºC and melting at 162−165 ºC, (lit. [ 90 ] 169 ºC). The latter proved by NMR to be fairly pure 2,4-dibromobenzoic acid ( 20 ) containing a few percent of p -bromobenzoic acid ( 26 ).…”

Preparation of Tyrian Purple (6,6′-Dibromoindigo): Past and Present

“…The 2,4-dibromobenzoic acid ( 67 ) required in this procedure is usually prepared via the hydrolysis of 2,4-dibromobenzonitrile ( 71 ) [ 147 , 148 , 149 , 150 , 151 , 152 , 153 , 154 , 155 , 156 ] or by the oxidation of 2,4-dibromotoluene ( 45 ) [ 157 , 158 , 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 ]. Unfortunately, neither of these methods is particularly attractive.…”

“…2,4-Dibromotoluene ( 75 ) is also a potential precursor for 2,4-dibromobenzoic acid ( 67 ). The former is usually prepared by multistep procedures [ 157 , 159 , 160 , 161 , 162 , 163 , 164 , 167 , 169 , 170 , 171 ], [for example, from 4-nitrotoluene ( 72 ) [ 160 , 164 , 170 ] ( Scheme 22 )], since direct bromination of 4-bromotoluene ( 20 ) ordinarily gives an 7:1 mixture of 75 and 3,4-dibromotoluene ( 76 ) [ 158 , 160 ] ( Scheme 23 ).…”

An Interpretation of Meta Orientation in the Alkylation of Toluene. The Relative Reactivity and Isomer Distribution in the Chloromethylation and Mercuration of Benzene and Toluene1,2

“…The yield of benzyl chloride is 65%, based on formaldehyde. Toluene was much more reactive-a 57% yield of the product was obtained in only 18 hours with half the quantity of the zinc chloride catalyst. In ease of manipulation and quality of product the procedure proved quite advantageous over that described by Blanc.45 Competitive experiments between toluene and (42) O. Grummitt and A. Buck, Org.…”