$RCHO + HS{O_3}Na \to $ $\mathop {\mathop {R{\text{ }} - {\text{ }}C{\text{ }} - {\text{ }}H}\limits^{\mathop {{\kern 1pt} |{\kern 1pt} {\kern 1pt} {\kern 1pt} }\limits^{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} OH} } }\limits_{\mathop {|{\kern 1pt} {\kern 1pt} }\limits_{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,S{O_3}Na} } R - CHO$

${C_6}{H_5}COC{H_3} + NaHS{O_3} \to $ No reaction