Two nice patents about protocatechualdehyde preparation were found on Espacenet.
Process for preparing protocatechualdehyde and its derivatives Patent US4165341 (http://l2.espacenet.com/dips/viewer?PN=US4165341&CY=gb&LG=en&DB=EPD)
Abstract
A process for preparing protocatechualdehyde or a 3-alkoxy-4-hydroxybenzaldehyde which comprises subjecting catechol or a 2-alkoxyphenol to reaction with glyoxylic acid in a basic aqueous medium in the presence of a catalyst containing one or more compounds selected from aluminium oxide, silicon oxide and hydrated aluminium oxide in an amount of not less than 0.01 g per 1 g of the starting catechol or 2-alkoxyphenol at a temperature of 0° to 50° C, and then oxidizing the thus obtained reaction mixture in a basic medium.
Process for preparing protocatechualdehyde Patent EP0786446 (http://l2.espacenet.com/dips/viewer?PN=EP0786446&CY=gb&LG=en&DB=EPD)
Abstract
Protocatechualdehyde is prepared by the steps of reacting piperonyl dichloride with molecular chlorine in the presence of phosphorus trichloride, phosphorus pentachloride or sulfuryl chloride to prepare dichloropiperonylidene dichloride and hydrolyzing the dichloropiperonylidene dichloride. The piperonyl dichloride can be prepared by the reaction of piperonal with thionyl chloride in the presence of DMF.
Life without chemistry would be a mistake.
Go to http://patft.uspto.gov/netahtml/srchnum.htm (http://patft.uspto.gov/netahtml/srchnum.htm)
and type in the US patent numbers 4165341 or 5696301 to see them. If you want to see the patent images too, click the "images" link at the top of the page.