Melting point discoloration

The submitters reported a yield of 5.8 g. (92%) of product as white needles, m.p. 53-54°. However, the checkers obtained colourless needles only after recrystallizing the product from hexane. The melting points of the discolored needles obtained initially by the checkers and the recrystallized material were the same. Melting points of 57° and 52-54° are recorded in the literature for ethyl thiazole-4-carboxylate. The spectral properties of the product are as follows infrared (chloroform) cm. 3130, 3030,... 

The zinc-dust treatment serves to reduce and remove small amounts of azo compounds (notably o-azobenzoic acid) which always discolor the crude product. Attempts to purify the crude product by crystallization from 33 per cent alcohol invariably led to a darker colored product with the same melting point as the crude. The decolorizing carbon is not intended to decolorize the solution but to clarify the filtrate before the precipitation of the diphenic acid. 

Diepoxyethylbenzene was first prepared by Everett and Kon (3) as a liquid which evidently was not pure because analysis showed a difference of 4% in the carbon content. Our product was a white crystalline mass with melting point 79°C. and boiling point 95°C. at 0.06 mm. Catalytic hydrogenation gave the theoretical absorption. The stabilizing effect in PVC mixtures was about 30% of dibutyltin laurate—i.e., 3.3 times more of the stabilizer is necessary to obtain the same discoloration as dibutyltin laurate in a plasticized mixture of PVC with 30% dioctylph-thalate at 200°C. for 20 minutes. 1,3,5-Triacetylbenzene was prepared by the two methods mentioned above. 

Dean-Stark trap. During this period the yellow reaction mixture turned first crimson and then dark brown. Toluene was removed under reduced pressure and the residual enamine crystallized from acetone as discolored crystals (8 g). The enamine (10 g) was treated with concentrated HC1 (1 ml) in methanol (200 ml). The crimson solution was evaporated and the residual dark oil crystallized from acetone, yielding the intermediate ketopyran (8.4 g, yellow needles from acetone). The crystals were added to methanol and an excess of sodium borohydride was gradually added to the solution, yielding on standard workup 7.47 g of the hydroxypyran. The crystalline hydroxy intermediate was well mixed with 4.5 g of anhydrous copper sulfate and heated to 150-160°C in a carbon dioxide current for 10 min. Upon cooling, the product was extracted into methylene chloride. Removal of the solvent under reduced pressure gave 6.3 g of discolored solid that was decolorized with carbon and recrystallized from acetone (melting point not reported). 

The melting point of 4-aminoveratrole obtained by reduction of 4-nitroveratrole is reported as 8 5-86°. The amine tends to discolor rapidly on exposure to air and light it should be stored in a sealed, dark container. 

Sorbitol will form water-soluble chelates with many divalent and trivalent metal ions in strongly acidic and alkaline conditions. Addition of liquid polyethylene glycols to sorbitol solution, with vigorous agitation, produces a waxy, water-soluble gel with a melting point of 35-40°C. Sorbitol solutions also react with iron oxide to become discolored. 

The furan dialdehyde is a stable colorless compound having a melting point of 110 °C. Contrary to furfural, even in the liquid state the furan dialdehyde does not undergo discoloration as it does not have the highly reactive hydrogen by which furfural polymerizes. At room temperature, furan dialdehyde is slightly soluble in water (10 g per liter at 17 °C) as well as in cyclohexane, hexane, ligroin, carbon tetrachloride, diethyl ether, and benzene. It is well soluble in ethanol, ethyl acetate, acetone, dimethylsulfoxide, and methylisobutyl ketone, as well as in hot water. 

Colorless liquid. M.p. —85°C. Polymerizes rapidly at the melting point to a clear glasslike mass which soon discolors to a yellow-red, brown and then cloudy substance. 

As shown in Tables 12.3 and 12.4, the thennal conductivities of dry layers of foods and pharmaceuticals are extremely low compared with the conductivities of insulators, such as cork and styrofoam. As a consequence, the temperatnre drop across the dry layer is large, and with surface tanperatures often limited to values below 65°C because of danger of discoloration and in some cases to values below 38°C because of the danger of denaturation, the resultant ice temperature is usually weU below -18°C. Except for materials with very low melting points, it is the surface temperature that limits the drying rate. 

One easily calculates that during the whole operation of the pile about 160 watt hours energy is dissipated in the form of ionization in a cm of diphenyl which is constantly in the pile. The above report describes diphenyl which has been exposed to 60 watt hours/cm radiation. The product is brownish, its melting point 58 C instead of 60°C and its average molecular weight 320 instead of 150. Apart from the discoloration, it shows to the naked eye no obvious sign of the harsh treatment it has received. 

When adding titanium compounds Shuster et al. [131] found that Ti(OBu)4 and Ti(OEt-NH-Et-NH2)3 caused torque reductions in blends with 10-30 wt % PCL, discoloration (white to red), gas evolution and foaming of the molten blend effects were more pronounced for Ti(OBu)4. In studying the Ti(OBu)4 system, Shuster et al. [131] noted that the uncatalysed physical blend with 25% PCL gave PC T at 220 °C and Tg 30 °C i.e. PCL plasticized PC and promoted crystallisation. Addition of 0.1% Ti(OBu)4 reduced the melting endotherm, broadened it and shifted it to lower temperatures (-210 °C) and broadened Tg. Addition of 0.2-0.3% Ti(OBu)4, caused the melting point to disappear and raised and sharpened Tg with 25% PCL the blend was transparent, but orange red the... 

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