Starting Materials-Impurities

In this Sect, we describe the starting material impurities and their effect on the processing and cure reactions of TGDDM-DDS epoxies. The cure reactions are characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) studies. The BF3 amine catalysts used to accelerate the cure of TGDDM-DDS epoxies are characterized by nuclear magnetic resonance (NMR) spectroscopy studies. 

The commercially available TGDDM, DDS and BF3 amine components all contain impurities, some of which may act as catalysts towards the cure reactions. 

FTIR studies indicate that commercial TGDDM (MY720, Ciba Geigy) contains 15-20% less epoxide groups than the pure tetrafunctional TGDDM epoxide molecule 9-U). Liquid chromatography studies indicate that the missing O 

Commercial DDS also contains a small percentage of a crystalline impurity as indicated by a DSC endotherm at 77 °C whose heat of fusion is 3 % of the total heat of fusion associated with the pure DDS m.pt at 165 °C 16). 

The impurities in the BF3 amine catalysts are highly variable and are discussed in detail in the following Sect. 3.3. 

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API = modified active pharmaceutical ingredient resulting from B and C B = starting material impurity with potential to form C and API ... 

Most colorants, because of their ionic (most dyes) or particulate (pigments) nature with strong intermolecular forces and low volatility cannot be analysed by GC, however, lower molecular weight species, such as certain starting materials, impurities, additives and breakdown products from colorants can be analysed. These include aromatic amines such as those in the German MAK III list, which were discussed earlier in this chapter in Section 10.2.2. 

Aluminum sulfate is a starting material in the manufacture of many other aluminum compounds. Aluminum sulfate from clay could potentially provide local sourcing of raw materials for aluminum production. Processes have been studied (24) and the relative economics of using clay versus bauxite have been reviewed (25). It is, however, difficult to remove impurities economically by precipitation, and purification of aluminum sulfate by crystallization is not practiced commercially because the resulting crystals are soft, microscopic, and difficult to wash effectively on a production scale (26—28). 

Chemical Properties. Stoichiometric vitreous sihca contains two atoms of oxygen for every one of sihcon, but it is extremely doubtful if such a material really exists. In general, small amounts of impurities derived from the starting materials are present and various stmctural defects can be introduced, depending on the forming conditions. Water is incorporated into the glass stmcture as hydroxyls. 

Because no process has been developed for selectively removing impurities in vanadium and vanadium alloys in the metallic state, it is essential that all starting materials, in aggregate, be pure enough to meet final product purity requirements. In addition, the consoHdation method must be one that prevents contamination through reaction with air or with the mold or container material. 

Whether or not any of these derivatives is likely to be satisfactory for the use of any particular case will depend on the degree of difference in properties, such as solubility, volatility or melting point, between the starting material, its derivative and likely impurities, as well as on the ease with which the substance can be recovered. Purification via a derivative is likely to be of most use when the quantity of pure material that is required is not too large. Where large quantities (for example, more than 50g) are available, it is usually more economical to purify the material directly (for example, in distillations and recrystallisations). 

Where larger quantities (upwards of Ig) are required, most of the impurities should be removed by preliminary treatments, such as solvent extraction, liquid-liquid partition, or conversion to a derivative (vide supra) which can be purified by crystallisation or fractional distillation before being reconverted to the starting material. The substance is then crystallised or distilled. If the final amounts must be in excess of 25g, preparation of a derivative is sometimes omitted because of the cost involved. In all of the above cases, purification is likely to be more laborious if the impurity is an isomer or a derivative with closely similar physical properties. 

When crude aulfonyl chlorides were used as starting materials, the reaction mixture was washed with a suitable solvent to remove organic impurities. In the case of higher-melting crystalline sulfonyl chlorides, heating to 50 may be necessary to complete their reduction. The solution of the sulfinate salt may be kept overnight, if desired, with no decrease in the yield of sulfonyl cyanide. 

Some aulfinates are commercially available. They may be used as starting materials for the preparation of aulfonyl cyanides also. Yields, however, are not significantly better than when the much cheaper and more readily available sulfonyl chlorides are used as starting materials. Good to excellent results are obtained, even when starting from rather impure sulfonyl chlorides. Illustrative examples are given in Table I. 

Conversion of 2-chloro-2-difluoromethoxy-l,lJ trifluoroethane to 2-difluo-romethoxy-l,l,l,2-tetrafluoroethane (98% purity) is accomplished with bromine trifluoride. The starting material is the major impurity [7] (equation 4)... 

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