Xylitol crystalline

A second monomethylene-xylitol has been reported by Schmidt and Nieswandt.80 It is a crystalline compound which was prepared from... 

Xylitol occurs as white crystals or as a crystalline powder. One gram dissolves in about 0.65 mL of water. It is sparingly soluble in ethanol. 

Meso configurations can have enantiomeric conformers in crystals. Ribitol and xylitol have meso configurations and are optically inactive in solution. In the crystalline state, they have the bent-chain enantiomorphic conformations. Xylitol crystallizes in space group P212121, so each crystal contains either only the optically active left-handed or the optically active right-handed conformers. There are, of course, an equal number of left- and right-handed crystals in any one batch, which on dissolution give no optical activity.1... 

Xylitol occurs as a white, granular solid comprising crystalline, equidimensional particles having a mean diameter of about 0.4—0.6 mm. It is odorless, with a sweet taste that imparts a cooling sensation. Xylitol is also commercially available in powdered form and several granular, directly compressible forms. See also Section 17. 

Compressibility see Figure 1. Crystalline xylitol, under the same test conditions as illustrated in Figure 1, produces 12.5 mm tablets of 40 N hardness at 20 kN compression force. 

Particle size distribution the particle size distribution of xylitol depends upon the grade selected. Normal crystalline material typically has a mean particle size of 0.4-0.6 mm. Milled grades are commercially available that offer mean particle sizes as low as 50 pm. Individual suppliers literature... 

Xylitol has a negative heat of solution that is far larger than that of other alternative sweetening agents see Table III. Because of this, xylitol produces an intense cooling effect as the crystalline material dissolves. Xylitol s combination of sweetness and cooling can create product appeal while helping to mask the undesirable taste of many pharmaceutical actives or excipients. 

A study of the relaxational transitions and related heat capacity anomalies for galactose and fructose has been described which employs calorimetric methods. The kinetics of solution oxidation of L-ascorbic acid have been studied using an isothermal microcalorimeter. Differential scanning calorimetry (DSC) has been used to measure solid state co-crystallization of sugar alcohols (xylitol, o-sorbitol and D-mannitol), and the thermal behaviour of anticoagulant heparins. Thermal measurements indicate a role for the structural transition from hydrated P-CD to dehydrated P-CD. Calorimetry was used to establish thermodynamic parameters for (1 1) complexation equilibrium of citric acid and P-CD in water. Several thermal techniques were used to study the decomposition of p-CD inclusion complexes of ferrocene and derivatives. DSC and derivative thermogravimetric measurements have been reported for crystalline cytidine and deoxycytidine. Heats of formation have been determined for a-D-glucose esters and compared with semiempirical quantum mechanical calculations. ... 

Thermal parameters affecting the crystallization of sorbitol have been studied depending on conditions, two crystalline modifications can arise, and a process for the rapid crystallization of molten sorbitol was proposed. Compression parameters of crystalline xylitol have also been reported. The viscosity of concentrated aqueous solutions of sodium and potassium halides in presence of D-mannitol has been studied the viscosity was related to the structure-making or structure-breaking effect of the salt in solution. ... 

Xylitol (IV), m.p. 61-61.5° (metastable modification), 93-94.5° (stable modification) tetraacetate, m.p. 62° is not found in nature despite the abundance of its parent aldose, n-xylose (wood sugar). Although xylitol has been known for over fifty years 17, 22), it had never been obtained crystalline until Wolfrom and Kohn 23) obtained the metastable form in 1942. Shortly thereafter the stable modification was reported by Carson, Waisbrot, and Jones 24), who were able to go from one form to the other at will. In the more recent work, D-xylose was reduced over nickel under pressure, whereas Fischer employed sodium amalgam. As pointed out by... 

In the pentitol series, xylitol on being heated with acids or with zinc chloride gives crystalline 1,4-anhydroxylitol and a sirupy dianhydro derivative, presumably with the 1,4 2,5-ring structure (6 ),... 

Acetonation of D-mannitol with 2,2-dimethoxyptDpane and p-toluenesulfonic acid in pyridine followed by in situ acetylation, then by isolation and deacetylation of the crystalline diacetate (1), has been recommended as a practicable procedure for the preparation of l,2 5,6-di-6>-isopropylidene-D-mannitoL Acrylates and methaciylates of xylitol diacetonides are referred b> in Chapter 7. 

The purity of xylitol can reach around 99.7% along witii a yield of 50-60% with a recovery method by concentration and solvent crystallization (Perez-Bibbins et al., 2013). However, the solvents used in these methods influence the solubility and crystalline behavior of xylitol. With a 99.8% purity, using activated charcoal followed by vacuum concentration and crystallization resulted in a cost-effective, simple, and environmentally friendly process (Misra et al., 2011). 

All the polyoles have proved to exhibit undesirable or dangerous side effects in animal studies and when used therapeutically in man this has led in some countries (such as Australia) to a proliibi-tion on the use of xylitol for intravenous nutrition. Large quantities of fructose and sorbitol lead to a metabolic acidosis, the severity of which cannot be foreseen, as well as hyperuricaemia, and reduction in hepatic stores of nucleotide-adenine and inorganic phosphates. Xylitol produces identical effects (with hyperuricaemia being particularly pronounced) as well as osmotic diuresis with loss of electrolytes and, in some cases, formation of crystalline deposits in the kidneys and brain. 

---