Sorbitol 2,4:3,5-dimethylene

A second dimethylene-D-sorbitol is also known it is the 2,4 3,5-compound (m. p. 192-193°), which was reported almost simultaneously by Haworth and Wiggins52 and by Hann, Wolfe and Hudson.44 In each case the synthesis involved the methylenation and subsequent saponification... 

Because PVP has substantial humectant properties (and thus tends to absorb moisture in high humidity, causing the applied gel to become very sticky), alcohols (e.g., SD alcohol 40, ethanol, sorbitol) can be added to alleviate this problem. The addition of more humidity-resistant copolymers of PVP, such as vinyl acetate copolymer, allows the product to have increased resistance to moisture absorption. However, curl-activating gel products function by actually attracting moisture to the hair with the use of humectant polyols such as dimethylene copolyol. 

Dimethylene pentaerythritol (m.p. 50°C, b.p, 230°C) may be o by the action of pentaeiythritol on formaldehyde solution in the j of zinc, chloride . It is reported to be more stable with respect to hy than diethyl ether. Tricyclicj formals are obtained as crystalline tates when mannitol and soibitol are heated with commercial forma and concentrated hydrochloric acid > . d-Sorbitol formal melts and d-mannitol formal at 227°C. These formals are only slightly in water. 

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