Bromination of naphthalene

Berliner et a/.284-8 have examined kinetics of bromination in aqueous acetic acid in an attempt to find the acid concentration at which the change in kinetic order principally occurs, though it follows from the earlier work that this will depend upon the aromatic reactivity. In 50 % acid the bromination of naphthalene was second-order overall284, and at constant ionic strength the rate coefficient showed a dependence on [Br-] according to equation (140)... 

This work is in its early stages, but it is already clear that a significant improvement in P-selectivity can be achieved by use of H zeolite Y as the catalyst for the bromination of naphthalene with tert-butyl hypobromite (Fig. 8) (ref. 11). It remains to be seen whether further improvements can be achieved by variation of the counterion or by variation of solvent. Such studies are currently in progress. 

The above method has been found to be more convenient and to give considerably better yields than that described previously.1 Bromination of naphthalene in carbon tetrachloride solution has also recently been described by Blicke.2... 

Answer By bromination of naphthalene via procedure XVi-l Thus, the synthesis of XVI-a becomes... 

Draw the seven resonance structures for the arenium ion formed in the bromination of naphthalene at the 1 position and the six resonance structures formed in bromination at the 2 position. 

Draw resonance structures of the intermediate carbocations in the bromination of naphthalene, and account for the fact that naphthalene undergoes electrophilic attack at Cl rather than C2. 

The reactions for the bromination of naphthalene in glacial acetic acid are given as ... 

As indicated in the third example in Table 6.13, the bromination of naphthalene (CioHg) produces a mixture (99 1) of C-1 (C-a) and C-2 (C-P) products even in the absence of iroa(lll) catalysts. Indeed, as shown, bromination can be effected in aqueous acetic acid (ethanoic acid, CH3CO2H). There is no reason to believe that the brominating agent is not bromine (Bt2) and that the process is not directly... 

Use a 500 ml. three-necked flask equipped as in Section IV,19, but mounted on a water bath. Place 128 g. of naphthalene and 45 ml. of dry carbon tetrachloride in the flask, and 177 g. (55 ml.) of bromine in the separatory funnel. Heat the mixture to gentle boiling and run in the bromine at such a rate that little, if any, of it is carried over with the hydrogen bromide into the trap this requires about 3 hours. Warm gently, with stirring, for a further 2 hours or until the evolution of hydrogen bromide ceases. Replace the reflux condenser by a condenser set for downward distillation, stir, and distil off the carbon tetrachloride as completely as possible. Mix the residue with 8 g. of sodium... 

CA Registry No 2493447-2. It is prepd by bromination of 5,6-dinitro-l,2,3,4-tetrahydro-naphthalene followed by dehydrobromination (Ref 20), from 2-nitro-l-naphthylamine by the same procedure as used for the prepn of the 1,4-isomer (Ref 20)... 

The medicinal importance of 2-aryltryptamines led Chu and co-workers to develop an efficient route to these compounds (130) via a Pd-catalyzed cross-coupling of protected 2-bromotryptamines 128 with arylboronic acids 129 [137]. Several Suzuki conditions were explored and only a partial listing of the arylboronic acids is shown here. In addition, boronic acids derived from naphthalene, isoquinoline, and indole were successfully coupled with 128. The C-2 bromination of the protected tryptamines was conveniently performed using pyridinium hydrobromide perbromide (70-100%). 2-Phenyl-5-(and 7-)azaindoles have been prepared via a Suzuki coupling of the corresponding 2-iodoazaindoles [19]. 

A different synthetic route involves halogenation (bromination, chlorination) of pyrene 77, which is thus converted to the tetrahalogen derivative. Oxidation with sulfuric acid to form a diperinaphthindandione with subsequent oxidation, once again in a sodium hydroxide solution [7], yields the tetra sodium salt of naphthalene tetracarboxylic acid 78 ... 

The presence of zeolite catalysts increases the amount of gaseous hydrocarbons produced during pyrolysis but decreases the amount of pyrolysis oil. Further, significant quantities of coke were formed on the surface of the catalysts in the course of pyrolysis. The catalysts reduced the yield of e.g., as styrene and cumene, in favor of naphthalene. The zeolite catalysts, especially Y-Zeolite, were found to be very effective in removing volatile organo bromine compounds. However, they were less effective in removing antimony bromide from the highly volatile products of pyrolysis (133). 

As methods of preparation, only the first three need be considered. It was decided not to try the direct action of bromine upon naphthalene, owing to the necessity of stirring the solid naphthalene and of collecting the hydrogen bromide gas the latter difficulty is also presented when carbon disulfide is used, and the objectionable properties of this solvent make its use further unfavorable. The third method, in which a suspension of naphthalene in alkaline hypobromite solution is treated with hydrochloric acid in aqueous solution, was found to give satisfactory results in so far as the yield of a-bromonaphthalene is concerned (though it was no better than with the method above described), but it presented considerable difficulties in the recovery of the hydrobromic acid. 

Further bromination of 3,4,6-tribromo-5-hydroxybenzo[6]thio-phene affords the 2,3,4,6-tetrabromo derivative in the absence of acetate ion, and 3,4,4,6-tetrabromo-4,5-dihydrobenzo[6]thiophen-5-one in the presence of acetate ion. 421 On treatment of 3,4-dibromo-, 4,6-dibromo-, 3,4,6-tribromo-, or 2,3,4,6-tetrabromo-5-hydroxybenzo-[6]thiophene with nitric acid in acetic acid, the corresponding unstable orange crystalline 4-bromo-4-nitro-4,5-dihydrobenzo[6]thio-phen-5-one is obtained.152,421 Hence, once both positions ortho to the hydroxyl group in 5-hydroxybenzo[6]thiophene are occupied by bromine, the properties of these compounds are analogous to the properties of l-bromo-2-naphthol which, on bromination in acetic acid in the presence of acetate ion, affords l,l-dibromo-l,2-dihydro-naphthalen-2-one whereas, in its absence, it affords l,6-dibromo-2-naphthol.616 The behavior of l-bromo-2-naphthol and its derivatives on nitration is similar to that of 4,0-dibromo-5-hydroxybenzo[6]thio-phene and its derivatives.162,616... 

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