Leather 103
they would have similar tanning properties. The first commercially success-
ful products were produced by sulfonating aromatic compounds containing
hydroxyl groups and then polymerising them with formaldehyde in what has
become known as the Nerodol process (Figure 8).
Later the Novolac process was developed in which the phenolic compound was
first polymerised and the product sulfonated to the required level (Figure 9).
HO OOHOHOHOHHO ORRO R
HOHOOH
OHOHHOHO
OH
OHnFigure 7Linking of flavanoid-based polyphenols to form condensed tannins
SO 3 HSO 3 HSO 3 HCH 2H 2 SO 4 HCHOFigure 8Outline of the Neradol method for syntan production