Composition of catalyst and solvent and catalysis processes using this composition

A catalytic composition, produced by a process comprising dissolving at least one Bronsted acid, designated HB, in a non-aqueous liquid medium with an ionic nature of general formula Q+A−, in which A− represents an anion that is identical to the anion B, and Q+ represents at least one compound of the formula -NR1R2R3R4+, PR1R2R3R4+, R1R2N═CR3R4+ and R1R2P═CR3R4+, where R1, R2, R3 and R4, identical or different, represent hydrogen or hydrocarbyl radicals having 1 to 12 carbon atoms with the exception, for NR1R2R3R4+, only one of R1, R2, R3 and R4 substituents represents hydrogen,

• a quatemary ammonium and/or phosphonium cation derived from nitrogenous or phosphorus heterocyclic compounds comprising 1, 2 or 3 nitrogen atoms and/or phosphorus atoms, of the formula:
• in which the cycles consist of 4 to 10 atoms, wherein R1 and R2 are defined as above;
• a quatemary ammonium and/or phosphonium cation of formula:
• R1R2+N═CR3—R5—R3C═N+R1R2, or
• R1R2P═CR3—R5—R3C═P+R1R2
• in which R1, R2 and R3, identical or different, are defined as above, and R5 represents an alkylene radical or a phenylene radical or SR1R2R3+, wherein R1, R2 and R3, identical or different, represent hydrocarbyl radicals that have 1 to 12 carbon atoms.