L. V. Afanas'eva

Ionic bromination of ethane and other alkanes (cycloalkanes) with bromine catalyzed by the polyhalomethane·2AlBr3 aprotic organic superacids under mild conditions

Abstract The polyhalomethane·2AlBr 3 aprotic organic superacids were shown to effectively catalyze low-temperature ionic bromination of (cyclo)alkanes. Ethane readily reacts with Br 2 at 55–65 °, affording mainly 1,2-dibromoethane. Propane, butane, and C 5 -C 6 cycloalkanes react at [fd9365-1], resulting in monobromides with high yields and good selectivity.

The first examples of selective carbonylation of n-butane and n-pentane

Abstract The polyhalomethane based superelectrophilic systems allowed us to accomplish the first efficient and selective carbonylation of n-butane and n-pentane with CO. Depending on the nature of the superelectrophilic system, Me 3 CCOOR or EtCH(Me)COOR (R = H, Alk) can be obtained at −20°C, 1 atm from n-butane and CO after water (or alcohol) treatment in ≈ 90% yield based on the superelectrophilic system. Pentane reacts with CO in the presence of the CBr 4 ·2AlBr 3 superacid to give a single product, EtC(Me) 2 COOR, in almost quantitative yield.

Functionalization of saturated hydrocarbons

Alkanes and cycloalkanes (isobutane, butane, isopentane, isohexane, and methylcyclopentane) react with benzene or bromobenzene at 0–20 °C in the presence of RCO+Al2X7− complexes (R=Me, Pr, or Ph; X=Cl or Br) to give products of the alkylacylation of arenes. The yields of alkylated aromatic ketones reach 60–87 % in 5–30 min, whereas the yields of unalkylated aromatic ketones (the competitive reaction) reach 0–40 %. The reactions of isobutane or isopentane with benzene result exclusively inpara isomers oft-BuC6H4COR or a mixture of Me2(Et)CC6H4COR and Me(i-Pr)CHC6H4COR isomers (1∶1), respectively. The reaction of isobutane with benzene also proceeds regioselectively and gives only one isomer, 2-Br-t-BuC6H4COR.

A new efficient and selective synthesis of ketones from alkanes or cycloalkanes, CO, and silanes in the presences of aprotic superacids

A new approach to the direct synthesis of ketones from alkanes or cycloalkanes (RH), CO, and silanes is proposed. Ketones were obtained in 50–97% yields from propane, butane, cyclopentane, cyclohexane, and methylcyclopentane on treatment with CO and silanes (Me4Si, Et4Si, orm- andp-XC6H4SiMe3, where X=Cl, Me, OMe) in the presence of CX4·2AlBr3 (X=Br, Cl) superacids at 0°C. The reactions withm- andp-XC6H4SiMe3 (X=Cl, Me) occur regioselectively to givem-ketones fromm-silanes andp-ketones fromp-silanes. However, the only product,p-MeOC6H4COR, is formed both fromm- andp-MeOC6H4SiMe3. The reaction ofcyclo-C5H9CO+ with BzSiMe3 results in an organosilicon ketone, Me3SiCH2C6H4COC5H9, while in the presence of an excess of an acylating system (after alcoholysis), Me2Si(OR′)CH2C6H4COR is formed.

Functionalization of saturated hydrocarbons by aprotic superacids 5. Regioselective carbonylation of propane in an organic solvent initiated by aprotic organic superacids CX4·nAlBr3 (X = Br, Cl;n = 1 or 2)

Aprotic organic superacids CX4 ·nAlBr3 (X = Br, CI; n = 1 or 2) are effective initiators of carbonylation of propane with CO in an organic solvent at -10 to -20 °C.

Functionalization of saturated hydrocarbons by aprotic superacids 4. Ionic bromination of ethane and other alkanes and cycloalkanes with molecular bromine in the presence of systems based on polyhalomethanes and AlBr3 under mild conditions

Aprotic organic superacids CBr4 · 2AlBr3, CBr4 · AIBr3, CHBr3 · 2AlBr3, CCl4 · 2AlBr3, and C6F5CF3 -2AlBr3 efficiently catalyze the bromination of alkanes and cycloalkanes with Br2. Ethane is selectively brominated at 55–65 °C to give mostly 1,2-dibromoethane (stoichiometric reaction). Propane, butane, cyclopentane, cyclohexane, and methylcyclopentane react with Br2 at -40 to -20 °C with good selectivity affording monobromides in high yields (catalytic reactions).

Nature of the species responsible for the high activity of RCOX·2A1X3 complexes in reactions with alkanes and cycloalkanes

The reasons for the high reactivity of aprotic organic superacids (AOS) containing an acyl halide and a double molar excess of Lewis acid in reactions with saturated hydrocarbons are studied. The synthesis and spectral properties of two pairs of acyl salts are studied: MstCO+AlBr4− and MstCO+Al2Br7− (Mst=2,4,6-Me3C6H2) and Ac+SbF6− and Ac+Sb2F11−. Comparison of the reactivities of these salts in cracking of alkanes and isomerization of trimethyl-enenorbornane demonstrated that the AOS activity is due to generation of acyl salts with a dimeric anion in the slightly polar solutions. Analysis of the13C NMR spectra suggests that the superacid properties of these salts are due to formation of species containing acyl cations coordinated to the Lewis acid.

Carbonylation of C7C8 cycloalkanes leading to individual tertiary carbonyl-containing compounds

Carbonylation of cycloheptane, methylcyclohexane, cyclooctane and ethylcyclohexane by CO in the presence of CBr4·2AlBr3 at −40°C and 1 atm was performed with good yields and selectivities. Individual esters of tertiary carboxylic acids of the cyclohexane series were the products of these cycloalkane carbonylations.

Isomerization of C12H20 tricyclanes into dimethyl- and ethyladamantanes by the action of complexes of acetyl bromide with aluminum bromide

It has been shown that AcBr·mAlBr3 complexes (m=1.8–2.0) effectively initiate the isomerization of C12H20 tricyclanes into a mixture of dimethyl- and ethyladamantanes. A quantitative conversion of the starting material is achieved in 3–5 min at room temperature, the overall yield of alkyladamantanes AdC2 amounting to 71–76%.

Isomerization of butane catalyzed by CH/sub 3/COX x 2A1X/sub 3/

ConclusionsAcX·2AlX3 (X=Br, Cl) are efficient catalysts for the isomerization of butane at room temperature. The activity of these catalysts is superior to that of known catalytic systems.