direct carboxylation reactions using co 2 under mild conditions a single step heterogeneous catalytic process for preparation of alkynyl carboxylic acids is disclosed application_number US 201314374338 A description the present invention provides a simple efficient reproducible environmental friendly m ii exchanged montmorillonite k 10 catalyst for the direct carboxylation reaction of compound of formula ii using co 2 in presence of base and solvent to obtain functionalized alkynyl carboxylic acids of general formula i in good yield and selectivity the group r in the formula represents a wide range of monovalent substituents selected from a group consisting of straight or branched alkyl straight or branched alkenyl straight or branched alkynyl straight or branched alkenyloxy straight or branched alkynyloxy straight or branched alkenylthio straight or branched alkynylthio aryl alkaryl aralkenyl aralkynyl aryloxy aralkoxy cycloalkyl heteroaryl a carbonyl where each of these may be substituted with halo hydroxyl nitro amino cyano alkoxy carboxyl ester alkyl alkenyl alkynyl thio sulfonyl sulfinyl phenyl heteroaryl or a carbonyl the terminal alkyne is represented by a formula r u2014 c u2261 c u2014 h where r in the formula represents a wide range of monovalent substituents selected from a group consisting of straight or branched alkyl straight or branched alkenyl straight or branched alkynyl straight or branched alkenyloxy straight or branched alkynyloxy straight or branched alkenylthio straight or branched alkynylthio aryl alkaryl aralkenyl aralkynyl aryloxy aralkoxy cycloalkyl heteroaryl a carbonyl where each of these may be substituted with halo hydroxyl nitro amino cyano alkoxy carboxyl ester alkyl alkenyl alkynyl thio sulfonyl sulfinyl phenyl heteroaryl or a carbonyl the product r u2014 c u2261 c.