Electrolyte for electrolytic capacitor, electrolytic capacitor and process for producing tetrafluoroaluminate salt of organic onium

An electrolytic solution for electrolytic capacitor, comprising a quaternary cyclic amidinium tetrafluoroaluminate represented by the following formula (1) and a solvent, and the electrolytic solution containing compounds represented by the following formulae (2) to (4) in a total amount of 0.6% by weight or less:

• wherein:
• each of R1 to R3 independently represents an alkyl group which may be substituted, a cycloalkyl group which may be substituted, an aryl group which may be substituted or an aralkyl group which may be substituted;
• X represents an alkylene group which may be substituted or an arylene group which may be substituted;
• or
• any of two selected from R1 to R3 and X may be connected together to form a ring, wherein the ring may have a nitrogen atom(s) in addition to the nitrogen atoms in the formula (1),
• wherein:
• each of R11 to R13 independently represents a hydrogen atom, an alkyl group which may be substituted, a cycloalkyl group which may be substituted, an aryl group which may be substituted or an aralkyl group which may be substituted;
• X1 represents an alkylene group which may be substituted or an arylene group which may be substituted;
• or
• any of two selected from R11 to R13 and X1 may be connected together to form a ring, wherein the ring may have a nitrogen atom(s) in addition to the nitrogen atoms in the formula (2),
• wherein the amino group may be protonated to form a salt,
• wherein:
• each of R22 and R23 independently represents a hydrogen atom, an alkyl group which may be substituted, a cycloalkyl group which may be substituted, an aryl group which may be substituted or an aralkyl group which may be substituted;
• X2 represents an alkylene group which may be substituted or an arylene group which may be substituted;
• or
• any of two selected from R22, R23 and X2 may be connected together to form a ring, wherein the ring may have a nitrogen atom(s) in addition to the nitrogen atoms in the formula (3),
• wherein the amidine group may be protonated to form a salt,
• wherein:
• each of R31, R33 and R34 independently represents an alkyl group which may be substituted, a cycloalkyl group which may be substituted, an aryl group which may be substituted or an aralkyl group which may be substituted;
• X3 represents an alkylene group which may be substituted or an arylene group which may be substituted;
• or
• any of two selected from R31, R33 and X3 may be connected together to form a ring, wherein the ring may have a nitrogen atom(s) in addition to the nitrogen atoms in the formula (4).