Peter H. Gore

The Friedel–Crafts acetylation of naphthalene in 1,2-dichloroethane solution. Kinetics and mechanism

The Friedel–Crafts acetylation of naphthalene, using acetyl chloride and aluminium chloride in 1,2-dichloroethane solution, has been studied kinetically. The α/β isomer ratio changes as a function of concentration of reactants, and time, e.g. from an initial 4–5 to a final 0.7. The results point to a different dependence for the two positions on the concentration of acylating reagent, AcCl, AlCl3, being second-order in this reagent for the α-reaction and first-order for the β-reaction. The rate of the α-reaction is impeded by the presence of free acetyl chloride, whilst the β-reaction is unaffected. The latter reaction exhibits activation parameters in the expected range, ΔH‡=ca. 48 kJ mol–1 and ΔS‡=ca.–99 J K–1 mol–1, whereas for the α-reaction ΔH‡=ca. 21 kJ mol–1 and ΔS‡=ca.–160 J K–1 mol–1 are both very low. Competitive and non-competitive kinetic hydrogen isotope experiments were carried out using [2H8]naphthalene. The mechanism for β-naphthyl acetylation is believed to involve a two-stage process, the second (loss of proton) being rate-limiting. The α-acetylation is believed to proceed through a σ-complex, from which elimination of HCl to give products is prevented for steric reasons; the reaction instead proceeds through a second σ-complex, decomposition of which is usually at least partly rate-limiting.

Friedel-crafts cyanation of some reactive aromatic hydrocarbons

Abstract Direct cyanation, using the heterogeneous Friedel-Crafts system cyanogen bromide/aluminium chloride, has given good yields of the following carbonitriles: anthracene-9-, chrysene-6-, 2-methyl-1-naphtho-, 4-methyl-1-naphtho-, 1-naphtho-, phenanthrene-9-, 2,4,6-trimethylbenzo-, triphenylene-1- and triphenylene-2-carbonitriles.

Friedel–Crafts reactions. Part XXV. Acetylation and benzoylation of iodobenzene and of o-, m-, and p-iodotoluenes

The Friedel–Crafts acetylation and benzoylation of iodobenzene and the isomeric iodotoluenes have been investigated in a range of solvents and at a range of temperatures. Under specific conditions good yields of p-iodoacetophenone or p-iodobenzophenone may be obtained. The reactivities of the iodotoluenes follow the sequence p- 2-iodo-4-methyl- > 2-iodo-6-methyl. In acylations p-iodotoluene gives very-low yields of 3-iodo-6-methylacetophenone only, or a mixture of 3-iodo-6-methyl- and 2-iodo-5-methyl-benzophenones; rearranged ketones, those formally derived from o-iodotoluene, are also formed. In addition all the iodo-substrates give by-products in major amounts: di-iodobenzenes, or di- and tri-iodotoluenes; aceto- or benzophenone, or the isomeric methylaceto- or methylbenzo-phenones. Acylations of o- and p-iodotoluenes also give isomeric chloromethylaceto-(or chloromethylbenzo-)phenones. Benzoylations carried out in ethylene chloride solution give low yields of 2-chloroethyl benzoate.

Friedel-crafts acetylation of durene,isodurene and prehnitene

Abstract Good yields of acetyl- and diacetyl-durene, acetyl- and diacetyl-isodurene, and acetylprehnitene can be obtained by Friedel-Crafts acylations. Products arising from methyl-migration prior to acetylation are also formed. A claim of the formation of diacetylprehnitene is shown to be incorrect.

Linear free energy relationships in the thiophene series. Part 3. A kinetic study of chlorine-isotopic exchange between lithium chloride and some 2-chloro-3-nitro-5-X-thiophenes

The rate constants for the chlorine-isotopic exchange between lithium chloride-36 and some 2-chloro-3-nitro-5-X-thiophenes (la—g) have been measured in sulpholane solution. The results obtained give a good Hammett correlation (in the range 323–373 K; calculated ρ 5.55—4.68), indicating that the charge developed in the transition state is strongly affected by the electronic effects of substituents. In order to study the effect of solvent on reactivity, the rates of 2-chloro-3,5-dinitrothiophene (lg) have also been measured in acetone, methanol, and propan-2-ol solutions. A comparison has been made between thiophene and benzene derivatives and the MNDO technique has been used to provide a theoretical model of the exchange reaction.

Acetyl exchange between acetylmesitylene and acetyl chloride under Friedel–Crafts conditions

The kinetics of acetyl exchange, catalysed by aluminium chloride, between acetylmesitylene and acetyl chloride have been determined for homogeneous solutions in nitromethane, and provide the first direct proof of reversibility in a classical Friedel–Crafts acylation.

Acetyl exchange between acetyl chloride and sterically hindered aryl ketones under Friedel–Crafts conditions

The kinetics of acetyl exchange between acetylmesitylene, or acetyldurene, and 14C-labelled acetyl chloride have been measured in nitromethane solution in the presence of aluminium chloride. Mechanistic studies using acetyl[3,5-2H2]mesitylene as substrate show conclusively that acetyl exchange proceeds, not by acylation–deacylation or deacylation–acylation, but via a synchronous reaction involving an ipso-complex. Theoretical calculations (MNDO) indicate that of three possible synchronous pathways, two are energetically feasible.

The Friedel–Crafts acetylation of naphthalene. Evidence for concurrent second- and third-order reactions

The Friedel–Crafts acetylation of naphthalene has been shown to give varying α : β isomer ratios as a function of concentration of the reactants. In consequence the ratio is strongly time- and temperature-dependent. Values of the α : β ratio (determined by an extrapolation procedure, for 1,2-dichloroethane solution) for the limit of zero reaction time, were plotted against reactant concentration, to give a straight line having a near-zero intercept. From this it is inferred that, whereas β-acetylation is essentially first-order with respect to the acylating reagent, α-acetylation is dominantly second-order in acylating reagent.

Friedel–Crafts acylations of aromatic hydrocarbons. Part XV. Acetylation of 2-methylnaphthalene

In the Friedel–Crafts acetylation of 2-methylnaphthalene all seven possible isomers are formed, their proportions depending on the experimental conditions. The yields of the isomers vary within the limits given in parentheses : 1 -(0·3–33%), 3-(0·8–14%), 4-(0·8–5·5%). 5-(0·4–2·0%), 6-(7·4–73%), 7-(4·2–58%), and 8-(9–59%). Competitive acetylation experiments in chloroform solution at 20° gave the following positional reactivities : 1-naphthyl 1·00, 2-naphthyl 0·31, 2-methyl-1-naphthyl 11·4, 2-methyl-3-naphthyl 0·31, 2-methyl-4-naphthyl 1·37, 2-methyl-5-naphthyl 0·19, 2-methyl-6-naphthyl 7·02, 2-methyl-7-naphthyl 1·78, and 2-methyl-8-naphthyl 16·1; the corresponding values obtained in nitromethane solution were: 1·00, 8·3, 6·9, 10·8, 6·1, 11·0, 177, 32·6, and 42·3, respectively. Overall and positional reactivities of 2,3-, 2,6-, and 2,7-dimethylnaphthalenes were calculated, and compared with results from earlier experiments.

A comparison of Friedel–Crafts acylations of acenaphthene and 1,8-dimethylnaphthalene. Methyl migration and acyl rearrangements accompanying acylations

Acylations of acenaphthene afford mixtures of 5-and 3-(but no 4-)acylacenaphthenes. The 5-acylacenaphthene : 3-acylacenaphthene ratio varies from 2 to 40 for acetylations, and from 3 to 13 for benzoylations, according to the solvent used. From benzoylations of 5-acetylacenaphthene two isomeric diketones could be isolated: 6-acetyl-3-benzoyl- and 3-acetyl-6-benzoyl-acenaphthene, the latter a product of acyl rearrangement. 1,8-Dimethylnaphthalene affords mixtures of 2-,3-, and 4-acetyl-1,8-dimethylnaphthalenes, together with two isomeric ketones, 3- and 4-acetyl-1,7-dimethylnaphthalenes, which result from methyl migration of the substrate. From competitive acetylations, the relative positional reactivities could be estimated for chloroform solution at 20 °C 1-naphthyl 1.0, 2-naphthyl 0.45, 1,8-dimethyl-4-naphthyl 60, 3-acenaphthenyl 6.4, and 5-acenaphthenyl 94.