Marschalk reaction

The Marschalk reaction is the sodium dithionite promoted reaction of a phenolic anthraquinone with an aldehyde to yield a substituted phenolic anthraquinone after the addition of acid.

The mechanism proposed by "Named Reactions in Organic Chemistry" is given in the google book reference^[1]

A somewhat more intuitive mechanism is provided below:

For those with academic licences here is one of the first good uses of the reaction^[2]

1. ^ http://books.google.com/books?id=ahRrPTfeqPEC&lpg=PA410&ots=ccHCAYlDoI&dq=marschalk%20named%20reaction&pg=PA411#v=onepage&q=&f=false
2. ^ http://www3.interscience.wiley.com/cgi-bin/fulltext/112354805/PDFSTART