a hydroxide group in the ring, excess base oxidizes the alcohol formed and acid can be prepared in high yields. on other hand, high yields of alcohol can be obtained from almost any aldehyde reduce the aldehyde by running the reaction in the present of formaldehyde. In this case, the formaldehyde reduces the aldehyde to alcohol and is itself oxidized to formic acid . In such a case, where the oxidant aldehyde differs from the reuctant aldehyde, the reaction is called the crossed Cannizzaro reaction. The Tollen's condensation includes a crossed Cannizzaro reaction as its last step. A Cannizzaro reaction run on 1,4-dialdehydes with a rhodium phosphine complex catalyst gives ring closure.