Previously reported work has indicated that pyridinium bromide perbromide (pyridine hydrobromide perbromide) can be considered a general brominating agent which may be used in brominations ordinarily performed with molecular bromine, such as substitution on aromatic rings and additions to double bonds (1). It is not a specific brominating reagent such as N-bromosuccinimide (2) which is recommended for brominating the allyl position of an olefin. However, the use of peroxide type catalysts (3,4) and aluminum or zinc chloride (5) have extended the scope of the brominations possible with N-bromosuccinimide. An excellent review of the reactions performed with brominating agents other than pyridinium bromide perbromide has been recently written by Carl Djerassi (6).Pyridinium bromide perbromide (7, 8) CsHeNBr • Brz is a red crystalline stable salt having the melting point 135-136°( dec.) with previous softening. The reagent has many advantages over dangerous liquid bromine. It is easily handled and stored and may be conveniently weighed. From its structural formula one would suspect that this perbromide can release free bromine, thus when substituted for bromine in any standard bromination the reaction should be expected to proceed in a normal manner. The experiments reported in this paper seem to verify the efficacy of pyridinium bromide perbromide as a substitute for bromine. The quantities of this reagent used were based on the presence of 45% available bromine, although the supplier has indicated 45-50% bromine available. EXPERIMENTAL Materials: The pyridinium bromide perbromide (PBPB) used in this study was supplied by Jasons Drug Company of Brooklyn, New York.6-Bromo-2-naphthol (9). /S-Naphthol (36 g., 0.25 mole) and 100 ml. of glacial acetic acid were placed in a 500-ml. round-bottom three-neck flask with a condenser, stirrer, and dropping-funnel. Pyridinium bromide perbromide (178 g.) was dissolved in 100 ml. of hot glacial acetic acid, and this solution -was added to the /3-naphthol through the droppingfunnel over a period of twenty minutes. The reaction was cooled slightly so as to effect a gentle reflux. The 0-naphthoI dissolved entirely as the addition took place. Then 25 ml. of water was added to the flask and the entire mixture heated to boiling. After Organic Syntheses (9), 39 g. of mossy tin was added and the mixture was refluxed for two hours. At the end of this period the mixture was cooled to 50°and filtered with suction.To the filtrate was added 1.5 liters of water. A copious white precipitate formed which was washed three times with divided portions of 250 ml. of water. Upon air-drying the solid, 25 g. of a slightly pinkish powder, m.p. 122-124°, was obtained; yield 45.5%. For the classical
The chemistry instructor usually assigns bromination reactions to the students after much deliberation and anxiety. This is quite understandable because of the hazards associated with bromine. The latter not only causes severe burns but the fumes produce a suffocating effect and are a source of much irritation. However, in the last few years various solid brominating agents have become commercially available, notably pyridinium bromide perbromide,1 2and N-bromosuccinimide.5 An excellent discussion of the reactions conducted with N-bromosuccinimide has been published.3Brominations with pyridinium bromide perbromide are safe and convenient. Since pyridinium bromide perbromide, C6Hf,NBr-Br2 is a relatively stable red crystalline compound/.5 having a melting point of 135-6°C. (dec.), there are no annoying fumes to contend with during handling; no elaborate apparatus is necessary for weighing out the required amounts of pyridinium bromide perbromide and when spilled it can be easily brushed off clothing, hands, or face with no accompanying danger of burns. Moreover, the student feels safer when handling "solid" bromine. In contrast to disagreeable and dangerous bromine, pyridinium bromide perbromide can be safely stored in the laboratory with no danger of spillage and annoyance to students and instructors.The brominations herein reported have been undertaken because they are usually the most common reactions performed in university and college laboratories. An attempt has been made to follow the normal procedures from the references indicated, but substituting pyridinium bromide perbromide for the bromine, assuming that the perbromide contained 45 per cent of available bromine. The manufacturer has reported 45 to 50 per cent bromine available. However, the lower limit has been utilized so as to insure complete bromination. From some of the reactions conducted it was evident that more than 45 per cent bromine was 1
Polymers of 3‐methoxybutyl acrylate (3‐MBA) were prepared by máss, solution, and emulsion polymerization techniques. The 3‐MBA polymers could be converted from soft, rubbery, soluble, thermoplastic films to hard, glossy, flexible, crosslinked films when exposed to air and/or transition metal catalysts at elevated temperatures. The crosslinked polymers are resistant to common organic solvents and to mineral acids. Strong alkalis degraded the crosslinked polymers. The second‐order transition temperature of poly‐3‐MBA is −56°C. as determined by volume dilatometry. A comparison of the crosslinking properties of poly‐3‐MBA and other alkyl and alkoxyalkyl polymers is discussed. An autoxidative mechanism is proposed for the crosslinking of 3‐MBA polymers.
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