Recrystallization seeding

The colorant is prepared by leaching the annatto seeds with an extractant prepared from one or more approved, food-grade materials taken from a hst that includes various solvents, edible vegetable oils and fats, and alkaline aqueous and alcohoHc solutions (46,47). Depending on the use intended, the alkaline extracts are often treated with food-grade acids to precipitate the annatto pigments, which ia turn may or may not be further purified by recrystallization from an approved solvent. Annatto extract is one of the oldest known dyes, used siace antiquity for the coloring of food, textiles, and cosmetics. It has been used ia the United States and Europe for over 100 years as a color additive for butter and cheese (48—50). 

Recrystallization of 96 from benzene afforded colorless prisms. That each crystal is chiral was shown by photochemical conversion into the optically active 97. Crystals of 96 which gave (+)- and (—)-97 on photocyclization have been tentatively identified as (+)- and (—)-crystals of 96, respectively. Large amounts of the (+)- and (—)-crystals of 96 can easily be prepared by seeding with finely powdered (+)- and (—)-... 

This liquid was hydrolyzed under conditions similar to those employed with d,L-arabitol pentaacetate and yielded a sirup which crystallized spontaneously on standing, or immediately if seeded with ribitol. The crude product melted at 96-104° upon recrystallization from ethanol the melting point and mixed melting point with an authentic sample of ribitol was 101.5-102°. 

Mechanical Separation of Crystals. The first instance of resolution was by L. Pasteur who was able to resolve crystals of sodium ammonium tartrate (which recrystallizes in two distinct, nonsuperimposable forms below 2TC). Although this procedure is rarely used, one might be able to seed a racemic solution resulting in only one... 

S7 The above CS2 solution from which Si 2 and most of the Sg has been crystallized at —78 °C is used for the preparation of S7, Sis and 820- Stirring of this solution at - 78 °C after addition of some glass powder (or seed crystals of S7) for about 2 hours results in the precipitation of finely powdered sulfur which is isolated by removing the solution by means of an immersion filter frit. The residue is extracted three times with small amounts of toluene (leaving an organe residue) from which S7 crystallizes on cooling to —78 °C. On recrystallization from CS2 pure S7 is obtained in 0.7% yield m.p. 39 °C... 

The main fraction melts at 41-43° (Note 8), and the other two fractions usually melt about a degree or two lower. The product is pure enough for most purposes it may be recrystallized from the minimal volume of alcohol necessary for solution at 45-50°. The solution is cooled to about 35° any oil which precipitates is brought back into solution by cautious addition of alcohol. The saturated solution is seeded, allowed to cool to room temperature, and then kept in a refrigerator for at least four hours. In this manner, 20-21 g. of flat, colorless needles is obtained the product melts at 42-43.50. 

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