P-Bromotoluene

Prepare a solution of p-tolyldiazonium chloride from 53 -5 g. of p-tolui-dine using the proportions and experimental conditions given under p-Chlorotoluene (Section IV,61). Add the diazonium chloride solution to the boiling cuprous bromide solution, and proceed as in Method 1. The yield of pure, colourless p-bromotoluene, b.p, 182-184° (mainly 183°), is 40 g. m.p. 26°,... 

For initial experience in the uae of Uthium, the preparation of either p-toluic acid or of a-napbtboic acid mcay be undertaken. For the former, p-bromotoluene is converted into the lithium derivative and the latter carbonated with soUd carbon dioxide ... 

The hydrolysis of p bromotoluene with aqueous sodium hydroxide at 300°C yields m methylphenol and p methylphenol in a 5 4 ratio What is the meta—para ratio for the same reac tion carried out on p chlorotoluene" ... 

Next ask yourself, "What is an immediate precursor of p-bromotoluene " Perhaps toluene is an immediate precursor because the methyl group would direct bromination to the ortho and para positions. Alternatively, bromobenzene might be an immediate precursor because we could carry out a Friedel-Cralts methylation and obtain a mixture of ortho and para products. Both answers are satisfactory, although both would also lead unavoidably to a product mixture that would have to be separated. 

Only one benzyne intermediate can form from p-bromotoluene two different benzyne... 

In a dry 3-1. three-necked, round-bottomed flask fitted with an efficient reflux condenser, a stirrer, a Y-tube holding a 1-1. and a 250-ml. addition funnel, and protected from moisture by calcium chloride tubes is placed 5.76 g. (0.237 mole) of magnesium turnings barely covered by anhydrous ether, p -Bromotoluene (40 drops) and ethyl bromide (20 drops) are added, and the reaction starts immediately. />-Bromotoluene (35.0 g., 0.205 mole) in 200 ml. of anhydrous ether is added at such a rate that reflux is maintained. To the resultant solution of />-methyl-phenylmagnesium bromide is added, over a 1-hour period, a solution of 25.4 g. (0.200 mole) of dichloroacetone in 200 ml. of anhydrous ether. 

There has been a very brief report on the use of [Ni(ii -C5Hj)Cl(NHC)]/NaQPr for the hydrodebromination of p-bromotoluene. As expected, the catalytic efficiency was carbene dependant (decreasing in the order IMes > SIMes > SIPr > IPr) although only a maximum yield of 40% was achieved. Interestingly, very similar catalytic efficiency was observed irrespective of whether the reaction was performed in refluxing THF at 65°C or in refluxing dioxane at 105°C [13]. 

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