A. V. Orlinkov

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.

CATIONIC POLYMERIZATION OF HYDROCARBON MONOMERS INDUCED BY COMPLEXES OF ACYL HALIDES WITH LEWIS ACIDS. 7. THE CRITERIA FOR CLOSENESS TO THE LIVING ST ATE FOR CATIONIC POLYMERIZATION OF ISOBUTENE

Two criteria for the quantitative estimation of “closeness to the living state” for polymerization systems in which an, important role belongs to elimination of a proton from the growing carbocation during cationic polymerization are proposed. The first criterion, (C=C)rel, is the proportion of units with C=C bonds in the polymer chains. The second criterion,kcl/kgr, is the ratio of the rate constants for proton elimination and chain growth. The criteria are used in experiments on the polymerization of isobutene in hexane and dichloromethane induced by complexes of acyl halides with aluminum bromide. Limitations and fields of application, of these criteria are examined.

CATIONIC POLYMERIZATION OF HYDROCARBON MONOMERS INDUCED BY COMPLEXES OF ACYL HALIDES WITH LEWIS ACIDS 8.* THE POLYMERIZATION OF ISOBUTYLENE IN THE PRE SENCE OF SUPERACIDS

AbstractThe polymerization of isobutylene inn-hexane at −78°C under the action of the superacid HBr·2A1Br3 as well as acetyl complexes MeCOBr·AlBr3 and MeCOBr·2AlBr3 in the presence of HBr·AlBr3 and HBr·2AlBr3, respectively, was studied. Unlike the superacid providing a quantitative yield of polyisobutylene (PIB) due to protonogenic initiation, the acetyl complexes suppress the proton initiation. In the presence of a mixture of both complexes with the superacid, only macromolecules with the head acetyl fragments MeC(O) are formed, which is evidence for a carbocationic initiation. The data obtained are explained by trapping of protons by the carbonyl groups to form ionic structures of then

Cationic polymerization of hydrocarbon monomers under the effect of complexes of acyl halides with lewis acids 3. Polymer chain initiation and breaking in hexane at -78‡C

begin{gathered} [Me - mathop Climits_parallel - PIB][Al_2 Br_7 ]^ - hfill HO^ + hfill end{gathered}

Cationic polymerization of hydrocarbon monomers under the effect of complexes of acyl halides with Lewis acids

n type (where PIB is polyisobutylene) and to suppress the ionization of the superacids due to the common ion effect.

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

The polarity of the solvent significantly affects polymerization of isobutylene under the effect of complexes of acetyl bromide with aluminum bromide of 1∶2 (Ac-2) and 1∶1 (Ac-1) composition. Going from hexane to the more polar CH2Cl2 is accompanied by an increase in the polymerization rates in both cases, a decrease in the molecular weight and molecular-weight distribution, and an increase in the ratio of C-Br/C=C groups in polyisobutylenes in both cases. In contrast to hexane, in CH2Cl2 the mechanism of initiation of the Ac-2 complex becomes nonselective, and only 42% of all of the polyisobutylenes contain head CO groups. The degree of efficiency of initiation by Ac-2 in CH2Cl2 is 100% (in comparison to 8.5% in hexane). The mechanism of initiation of polymerization by the Ac-1 complex is the same in hexane and in CH2Cl2. Polyisobutylenes containing no head carbonyl groups are obtained in both cases.

CATIONIC POLYMERIZATION OF HYDROCARBON MONOMERS INDUCED BY COMPLEXES OF ACYL HALIDES WITH LEWIS ACIDS : 10.* THE INFLUENCE OF THE COMPOSITION OF COMPL EXES OF MESITOYL BROMIDE WITH ALUMINUM BROMIDE ON THEIR ABILITY TO INITIATE ISOBUTYLENE POLYMERIZATION

Polymerization of isobutylene under the effect of the AcBr·2AlBr3 (Ac-2) complex in hexane at −78‡C has some characteristics of “living” polymerization; however, in contrast to truly “living” polymerization, the process is characterized by high values of Mw/Mn and continuously occurring chain breaking. The steady-state concentration of active polymerization sites is established at the very beginning of the process; the dependence of the number of active sites on the starting concentration of Ac-2 is in agreement with the hypothesis concerning initiation by free acyl cations. The features of polymerization under the effect of the AcBr-AlBr3 (Ac-1) complex are characteristic of cationic polymerization processes.

Functionalization op saturated hydrocarbons in the presence of aprotic organic superacids. 2. Single-stage synthesis of thioesters R1CO-SR from n-alkanes or cycloalkanes (RH), elemental sulfur, and complexes R1COBr·-2AlBr3

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%.