Purity intermediate compounds

The tetrafluorocobaltates of the alkali metals show12 considerable differences in their reactions with benzene. Lithium tetrafluorocobaltate(III) at 100-130 C gives 3,3,6,6-tetra-fluorocyclohexa-1,4-diene (13) of over 90% purity. This compound has long been postulated1,549 as a major intermediate in the fluorination with cobalt(III) fluoride. The sodium, potassium, and rubidium salts give similar product mixtures (ca. 8 compounds), most being polyfluoroenes (e.g. 14, 8% 15, 12% 16, 35%). 

The efficiency of drug production will depend on being able to identify and assess the chemical purity of the drug and also that of the intermediate compounds involved at each step in the synthesis. This means that it is normally... 

The specific activity of 357 was 2.09 GBq mmol-1 and the radiochemical purity >97%. The overall radiochemical yield from potassium [14C]cyanide was 16% (150.5 MBq). The NMR spectra of intermediate compounds indicated that the reactions of equation 152 yielding 357 proceeded with complete retention of configuration at the chiral centre at C(8). In the reaction of RC1 with Na14CN, the S 2 displacement occurred with an overall retention of configuration due to participation of the nitrogen ring336,338. 

Discovery chemists measure or estimate the purities of the compounds they make, not only from training or habit but always with good reason. Their reasons concern the fates of the samples, which depend on whether the substances represent target or intermediate compounds. 

As shown in Fig. 3.16, disulfide-functional initiator was prepared through a five-step synthesis. Figures 3.17 and 3.18 confirm the high purity of the initiator and the intermediate compounds. As calculated in Fig. 3.17, the integral area ratio of peak (a), peak (i) and peak (d+e) is 1.00/3.10/4.09, in consistency with its theoretical ratio of 1.00/3.00/4.00. Using this functional initiator. Seesaw-type polystyrene macromonomer =-S-S-(PS-Br)2 was successfully prepared by ATRP, and its typical NMR spectrum is shown in Fig. 3.19. 

The theory of sublimation, t.e. the direct conversion from the vapour to the sohd state without the intermediate formation of the liquid state, has been discussed in Section 1,19. The number of compounds which can be purified by sublimation under normal pressure is comparatively small (these include naphthalene, anthracene, benzoic acid, hexachloroethane, camphor, and the quinones). The process does, in general, yield products of high purity, but considerable loss of product may occur. 

The composition of the products from the isomerization of an unsaturated compound under the influence of a catalytic amount of a base is governed by the relative thermodynamic stabilities of the starting compound and the product. Of particular synthetic interest are isomerizations in which there is an accumulation of an isomer in the isomerization sequence. Isolation of the desired intermediate in a reasonable state of purity is often a matter of careful selection of the base and the solvent. The following reactions are representative examples ... 

Production figures for the aminophenols are scarce, the compounds usually being classified along with many other aniline derivatives (86). Most production of the technical grade materials (95% purity) occurs on-site as they are chiefly used as intermediate reactants in continuous chemical syntheses. World production of the fine chemicals (99% purity) is probably no more than a few hundred metric tons yearly, at prices of about 45 per kg in 1990. 

Fewer procedures have been explored recently for the synthesis of simple six-membered heterocycles by microwave-assisted MCRs. Libraries of 3,5,6-trisubstituted 2-pyridones have been prepared by the rapid solution phase three-component condensation of CH-acidic carbonyl compounds 44, NJ -dimethylformamide dimethyl acetal 45 and methylene active nitriles 47 imder microwave irradiation [77]. In this one-pot, two-step process for the synthesis of simple pyridones, initial condensation between 44 and 45 under solvent-free conditions was facilitated in 5 -10 min at either ambient temperature or 100 ° C by microwave irradiation, depending upon the CH-acidic carbonyl compound 44 used, to give enamine intermediate 46 (Scheme 19). Addition of the nitrile 47 and catalytic piperidine, and irradiation at 100 °C for 5 min, gave a library of 2-pyridones 48 in reasonable overall yield and high individual purities. 

Several alkylboranes are available in enantiomerically enriched or pure form and can be used to prepare enantiomerically enriched alcohols and other compounds available via organoborane intermediates.196 One route to enantiopure boranes is by hydroboration of readily available terpenes that occur naturally in enantiomerically enriched or pure form. The most thoroughly investigated of these is bis-(isopinocampheyl)borane (Ipc)2BH), which can be prepared in 100% enantiomeric purity from the readily available terpene a-pinene.197 Both enantiomers are available. 

DAS (11.7) is synthesised from 4-nitrotoluene-2-sulphonic acid (11.6) by the route outlined in Scheme 11.1. An important factor in the preparation of DAST brighteners in the purity necessary for good performance is the purity of the DAS used as starting material. At one time DAS made in this way contained significant amounts of yellow azoxy compounds similar to 11.8, which formed the main components of the obsolescent dye Sun Yellow (Cl Direct Yellow 11) made by the partial reduction and self-condensation of intermediate 11.6. Today the major manufacturers supply DAS essentially free from these undesirable impurities [37]. 

---