Formaldehyde → (2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanal

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1500 g of the 37% formalin solution of Example 1 (18.5 moles formaldehyde) and 491 g of cyclohexanone (5 moles) are heated with stirring to 95° C., followed by the addition of 56 g of a 50% aqueous solution of the formose used as co-catalyst in Example 1 of German Offenlegungsschrift No. 2,639,084 and 15 g of lead acetate trihydrate. The pH-value of the mixture is adjusted to 7.5 by the addition of 10% sodium hydroxide. After the reaction has started (increase in the temperature of the mixture to 100°-102° C.), the pH is kept between 6.5 and 7.0 by the addition of more sodium hydroxide. After about 20 minutes, the reaction is stopped at a residual formaldehyde content of 1.5% by cooling with ice water. Total consumption of 10% sodium hydroxide: 123 g. Most of the lead is precipitated with 10 g of sodium bicarbonate and the solution is fully desalted over ion exchangers after the deposit has been filtered off under suction. 800 g of a modified formose having a water content of 5.8% and a sugar content (expressed as glucose) of 37% are obtained.

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