Synthetic lubricating oil

A synthetic lubricating oil comprising one or more cyclic ketals or cyclic acetals represented by the general formula (V) or (VI):

• ##STR34## wherein R.sup.3 represents a hydrogen atom or a linear, branched, or cyclic alkyl group having 1-12 carbon atoms, R.sup.4 represents a linear, branched, or cyclic alkyl group having 1-12 carbon atoms, with the proviso that R.sup.3 and R.sup.4 are not both methyl, or R.sup.3 and R.sup.4 together may represent an alkylene group having 2-13 carbon atoms, a total carbon atoms of R.sup.3 and R.sup.4 being 1-13.

A working fluid composition for a refrigerating machine comprising a refrigeration oil containing cyclic ketals or cyclic acetals and a hydrofluorocarbon, wherein the hydrofluorocarbon and the refrigerating oil are contained at hydrofluorocarbon/refrigerating oil (weight ratio) of 50/1 to 1/20, wherein said cyclic ketals or cyclic acetals are obtained by a reaction between one or more polyhydric alcohols having an even number of hydroxyl groups of not less than 4 and not more than 8 and one or more of Compound C or D, wherein the Compound C is a carbonyl compound represented by the general formula (II):

• ##STR35## wherein R.sup.3 represents a hydrogen atom or a linear, branched, or cyclic alkyl group having 1-12 carbon atoms;
• R.sup.4 represents a linear, branched, or cyclic alkyl group having 1-12 carbon atoms;
• R.sup.3 and R.sup.4 together may represent an alkylene group having 2-13 carbon atoms, a total carbon atoms of R.sup.3 and R.sup.4 being 1-13, and wherein Compound D is ketals or acetals obtained by a reaction between the carbonyl compound represented by the general formula (II) and a lower alcohol having 1-6 carbon atoms.

Cyclic acetals represented by the following general formula (i) or (ii):

• ##STR36## wherein R.sup.5 represents a hydrogen atom, and R.sup.6 represents a branched alkyl group having 3 carbon atoms or a linear or branched alkyl group having 4-21 carbon atoms;
• or
• R.sup.5 represents a linear or branched alkyl group having 1-21 carbon atoms, and R.sup.6 represents a linear or branched alkyl group having 2-21 carbon atoms.