Preferred are methyl formate, ethyl formate, propyl formate, butyl formate, isobutyl formate, pentyl formate, and the like. Most preferred is ethyl formate. 

The ethers are not particularly restricted, and may be cyclic or acyclic, or saturated or unsaturated. But saturated ones are preferably used in general. Generally, ones con› taining 3 to 20 carbon atoms, preferably 4 to 12 carbon atoms and more preferably 4 to 8 carbon atoms are used. As specific examples, there may be mentioned, for example, diethyl ether, methyl tert-butyl ether, dipropyl ether, diiso› propyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, anisol, phenetole, butyl phenyl ether, methoxytoluene, dioxane, furan, 2-methylfuran, tetrahydro› furan, tetrahydropyran, ethylene glycol dimethyl ether, eth› ylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol mono› ethyl ether, ethylene glycol monobutyl ether, and the like. Preferred are diethyl ether, methyl tert-butyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, anisol, phenetole, butyl phenyl ether, methoxytoluene, dioxane, 2-methylfuran, tetrahydrofuran, tetrahydropyran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and the like. More pre› ferred are diethyl ether, methyl tert-butyl ether, anisol, dioxane, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and the like. Still more preferred are diethyl ether, methyl tert-butyl ether, anisol, and the like, and most preferred is methyl tert-butyl ether. 

The alcohols are not particularly restricted but may be cyclic or acyclic, or saturated or unsaturated. Saturated ones are generally preferred, however. Generally, ones containing 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, and still more preferably 1 to 6 carbon atoms are used. 35 Among them, monohydric alcohols containing 1 to 5 carbon atoms, dihydric alcohols containing 2 to 5 carbon atoms, and trihydric alcohols containing 3 carbon atoms are preferred. 

As specific examples of these alcohols, there may be mentioned, for example, monohydric alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-bu› tanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pen› tanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-oc› tanol, 2-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, ally! alcohol, propargyl alcohol, benzyl alcohol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 4-methylcy- clohexanol, and the like; dihydric alcohols such as 1,2- ethanediol, 1,2-propandiol, 1,3-propandiol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pen› tanediol, and the like; and trihydric alcohols such as glyc› erol, and the like. 

As the monohydric alcohols, preferred are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pen- tyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexa- no!, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1- butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-unde› canol, 1-dodecanol, benzyl alcohol, cyclohexanol, 1-meth› ylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexa- no!, 4-methylcyclohexanol, and the like. More preferred are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-bu- 

tanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pen› tanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, cyclohexanol, and the like. Still more preferred are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, iso› pentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neo- pentyl alcohol, and the like. Particularly preferred are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-bu› tanol, isobutyl alcohol, 2-methyl-1-butanol, isopentyl alco› hol, and the like. Most preferred is 2-propanol. 

As the dihydric alcohols, preferred are 1,2-ethanediol, 1,2-propandiol, 1,3-propandiol, and the like. Most preferred is 1,2-ethanediol. As the trihydric alcohols, glycerol is preferred. 

As fatty acids, there may be mentioned, for example, formic acid, acetic acid, propionic acid, and the like. Pre- ferred are formic acid and acetic acid, and most preferred is acetic acid. 

The ketones are not particularly restricted, and ones having 3 to 6 carbon atoms are preferably used. As specific examples, there may be mentioned, for example, acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, and the like. Preferred are acetone and methyl ethyl ketone, and most preferred is acetone. 

The nitriles are not particularly restricted, and may be cyclic or acyclic, or saturated or unsaturated. However, saturated ones are preferably used in general. Generally, ones containing 2 to 20 carbon atoms, preferably 2 to 12 carbon atoms, and more preferably 2 to 8 carbon atoms are used. 

As specific examples, there may be mentioned, for example, acetonitrile, propiononitrile, malononitrile, buty› ronitrile, isobutyronitrile, succinonitrile, valeronitrile, glu› taronitrile, hexanenitrile, heptylcyanide, octylcyanide, unde› canenitrile, dodecanenitrile, tridecanenitrile, pentadecanenitrile, stearonitrile, chloroacetonitrile, bromo- acetonitrile, chloropropiononitrile, bromopropiononitrile, methoxyacetonitrile, methyl cyanoacetate, ethyl cyanoac- etate, tolunitrile, benzonitrile, chlorobenzonitrile, bro› mobenzonitrile, cyanobenzoic acid, nitrobenzonitrile, anisonitrile, phthalonitrile, bromotolunitrile, methyl cya› nobenzoate, methoxybenzonitrile, acetylbenzonitrile, naph› thonitrile, biphenylcarbonitrile, phenylpropiononitrile, phe- nylbutyronitrile, methylphenylacetonitrile, diphenylacetonitrile, naphthylacetonitrile, nitrophenylac› etonitrile, chlorobenzylcyanide, cyclopropanecarbonitrile, cyclohexanecarbonitrile, cycloheptanecarbonitrile, phenyl› cyclohexanecarbonitrile, tolylcyclohexanecarbonitrile, and the like. 

Preferred are acetonitrile, propiononitrile, succinonitrile, butyronitrile, isobutyronitrile, valeronitrile, methyl cyano- acetate, ethyl cyanoacetate, benzonitrile, tolunitrile and chloropropiononitrile. More preferred are acetonitrile, pro› piononitrile, butyronitrile and isobutyronitrile, and most preferred is acetonitrile. 

As the nitrogen compounds other than nitriles, there may be mentioned, for example, amides such as formamide, N-methylformamide, N, N-dimethylformamide, N,N-dim› ethylacetoamide, N-methylpyrrolidone, and nitromethane, triethylamine, pyridine, and the like. 

As the sulfur compounds, there may be mentioned, for example, dimethyl sulfoxide, sulfolane, and the like. 

In selecting the organic solvent to be used from among the organic solvents mentioned above, such properties as boil- 

