The preparation of acenaphthylene from acenaphthene. II. The vapour phase catalytic dehydro-genation of acenaphthene
✍ Scribed by Kynaston, Walter ;Jones, J. Idris
- Book ID
- 102889628
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1949
- Weight
- 782 KB
- Volume
- 68
- Category
- Article
- ISSN
- 0368-4075
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✦ Synopsis
product, polymonoucefoxy-ucenaphfhylene to analysis, giving the following -results (Found: 1.75% ash, C 80.4; H 4.3; CH3C0, 20.3% on the ash-free material. (CtoHIo02),I requires Photochemical hdogenadon of acenaphthene Bromination of acenaphthene occurred readily and with copious evolution of hydrogen bromide when the experiment was conducted in the open in bright sunshine. A solution of bromine (16 g.) in carbon tetrachloride (100 ml.) was slowly added to a gently boiling solution of acenaphthene (15.4 g.) in the same solvent (100 ml.) contained in a Pyrex flask attached to a reflux condenser. Bromination was complete in about 20 minutes. The final solution was cooled in the refrigerator, but no crystalline material separated. On removing the solvent by distillation 23.4 g. of a yellowish oil, which could not be induced to crystallize, was obtained. During an attempt to distil the oil, decomposition with evolution of hydrogen bromide set in and the product which distilled was a yellow crystalline solid (8 9.) which was identified as acenaphthylene. It was obvious, therefore, that, under the above conditions, some, if not all, of the bromine had entered the five-membered ring and not the aromatic nucleus. The bromination reaction was repeated, the carbon tetrachloride solution was washed with ro% sodium carbonate solution to remove free hydrogen bromide and, after drying over calcium chloride, the solvent wes removed under reduced pressure. Again, the same yield of yellowish oil was obtained. A halogen determination (Carius) on a sample of the freshly prepared material showed Br, 34.2, 34.15'7& C,,H,Br requires Br 34 -3% corresponding to a monobromoacenaphthene. A stable picrate could not be prepared from the oil, decomposition with liberation of hydrogen bromide taking place on warnling the solution with picric acid. The only crystalline material isolated was accnaphthylene picrate, no trace of 5-bromoacenaphthene picrate being found. On oxidation with chromic acid in acetic acid the oil (5 g.) yielded naphthalic anhydride (4.2 g.) indicating that all the bromine was located in the 1-position. The product of photochemical bromination of acenaphthene is, therefore, exclusively 1-6romoace~~aphthene. This was confirmed by the complete removal of bromine from a freshly prepared sample by alcoholic potassium hydroxide. I-Bromoacenaphthene is not stable, it cannot be distilled wen under a pressure of 5 mm. At room temperature, either alone or in solution, it slowly dehydrobrominates, giving a polymeric form of acenaphthylene, soluble in benzene and chloroform, insoluble in alcohol and ether. Under the influence of the liberated hydrogen bromide thc acenaphthylene, which is first formed, polymerizes to give what Dziewonski termed the acid polymer together with some biacenaphthylidene-the dimcr of acenaphthylene. The polymer is obtained as a pale yellowish amorphous powder when a benzene solution of the I-bromo compound, which has been standing for some time, is poured into excess alcohol. It is contaminated with biacenaphthylidene and exhibits the characteristic blue fluorescence of this compound. Its melting point is in the range 160-170" and is very indefinite.
Acenaphthene (15.4 g.) was brominated under the same conditions with two moles of bromine (32 g.). In this case a yellow crystalline material separated on cooling the solution remaining after partial removal of the solvent under reduced pressure. By recrystalhation from ether I : 2-dibromoacenauh-C 80.0, H 4-79 CHSCOy 20.5%).
. sunshine to a solution of acenaphthene (IS -4 g.) in the same solvent (100 d.) at atmospheric temperature. Chlorination was rapid and hydrogen chloride was fteely evolved. On removing the solvent under reduced pressure I-chloroacenaphthene was obtained as a pale yellow unstable oil, losing hydrogen chloride on standing and yielding a polymeric form of acenaphthylene. It was nnalysed by the Carius method. (Found : c118.6,18.8 C,,H,CI requires C118.8%.) All the chlorine could be removed by treatment with alcoholic potash and a nearly quantitative yield of naphthalic anhydride was obtained by oxidation with chromic acid in acetic acid solution, thus confirming the orientation. Acknowledgment
The work described in this paper forms part of the programme of investigation of the Chemistry Research Board and is published by permission of the Director,