Chemical workup

However, pyrolysis is rapid, avoids sample wet chemical workup, avoiding sample loss and contamination, and has a low sample requirement. It allows the determination, in a single step, of polymeric materials (with in situ hydrolysis of the hydrolysable polymers and thermal decomposition of the nonhydrolysable polymers) and low molecular weight components [16]. As a result, pyrolysis is a relatively fast and inexpensive technique, especially if compared with the classical wet analytical procedures that are required prior to GC/MS analyses. 

Of course, the goal of every synthetic organic chemist is to obtain crystalline products, and a few cases of crystalline synthetic proteins have been reported. These include the ribonuclease A synthesized in solution/35 which crystallized after chemical workup and affinity chromatography (see Section 5.1.6.2.2). Further examples include an HIV protease analogue/701 a ubiquitin analogue/59 and monellin/89 which were each prepared by solid-phase methods and purified by HPLC. 

Field desorption analysis therefore offers an opportunity to survey biological extracts for abnormal distributions of these compounds without necessitating extensive chemical workup. 

Preliminary tests, color reactions, and spot tests [10.7] were formerly used to identify individual resins but are no longer important because they are not sufficiently specific and they do not provide quantitative results. They have been largely replaced by modern spectroscopic and chromatographic methods, which often require preliminary chemical workup of the sample. 

Chemical Workup. Chemical decomposition of resins followed by qualitative and quantitative analysis is still an important technique because, apart from NMR spectroscopy, none of the instrumental analytical methods provides reliable quantitative values. Chemical workup is also essential for low concentrations of resin building blocks that are often unknown it simplifies and enables the desired substances to be concentrated. Qualitative and quantitative determination is carried out by instrumental methods. 

Chemicals responsible for odor in some PUR foams were synthesised by polymerisation of PO in CH2CI2 with Bp2(C2H )20 catalyst (114). The yield was 25% volatile material and 75% polymeric material. The 25% fraction consisted of dimethyldioxane isomers, dioxolane isomers, DPG, TPG, crown ethers, tetramers, pentamers, etc, and 2-ethy1-4,7-dimethyl-1,3,6-trioxacane (acetal of DPG and propionaldehyde). The latter compound is mainly responsible for the musty odor found in some PUR foams. This material is not formed under basic conditions but probably arises during the workup when acidic clays are used for catalyst removal. 

A careful assessment of the constitution of compound 10 led to the development of a rather efficient strategy featuring the Diels-Alder reaction (see Scheme 3). Although the unassisted intermole-cular reaction between 3-hydroxy-2-pyrone (16)23 and a,/ -unsatu-rated ester 17 is unacceptable in terms of both regioselectivity and chemical yield, compounds 16 and 17 combine smoothly in refluxing benzene and in the presence of phenylboronic acid to give fused bicyclic lactone 12 (61% yield) after workup with 2,2-... 

Besides simple alkyl-substituted sulfoxides, (a-chloroalkyl)sulfoxides have been used as reagents for diastereoselective addition reactions. Thus, a synthesis of enantiomerically pure 2-hydroxy carboxylates is based on the addition of (-)-l-[(l-chlorobutyl)sulfinyl]-4-methyl-benzene (10) to aldehydes433. The sulfoxide, optically pure with respect to the sulfoxide chirality but a mixture of diastereomers with respect to the a-sulfinyl carbon, can be readily deprotonated at — 55 °C. Subsequent addition to aldehydes afforded a mixture of the diastereomers 11A and 11B. Although the diastereoselectivity of the addition reaction is very low, the diastereomers are easily separated by flash chromatography. Thermal elimination of the sulfinyl group in refluxing xylene cleanly afforded the vinyl chlorides 12 A/12B in high chemical yield as a mixture of E- and Z-isomers. After ozonolysis in ethanol, followed by reductive workup, enantiomerically pure ethyl a-hydroxycarboxylates were obtained. 

Balance all chemical equations in the plan taking into workup reactions as appropriate and arrange these in the appropriate reaction stages. 

Cost factor. The calculation of CE is similar to current approaches of LCC analyses, again tailored to the evaluation of chemical synthesis strategies. CE includes (i) the costs of the supply of reactants, solvents and auxiliaries (ii) costs resulting from synthesis, (iii) workup, (iv) application and (v) disposal. Again, this effort is related to the molarity (or mass) of the product. 

Thus, when acid 76 was crystallized as a salt with (S)-(-)-l-phenylethylamine ([S]-PEA), the X-ray structure showed that the conformational enantiomer 76a was trapped in the crystal, displaying O - H and O - Ht distances of 2.47 A and 3.41 A, respectively. The conformation of 76a placed the carbonyl oxygen and Hj, closer to the ideal values mentioned in Figure 7.26 as compared to H. A significant preference for Hj, was demonstrated after photolysis at 0 °C and diazomethane workup, when ester 77a (B) was obtained in 65% ee after 90% conversion. Figure 7.27 illustrates the minimal atomic displacements required for reaction by comparing the X-ray structure of the reactant with that of the product, and with a structure obtained at 50% conversion. Better chemical results were obtained by photolysis of 76a with (/ )-CEA, which gave 90% ee of ester of 77a (B) after diazomethane workup. 

Approximately 60 g of Raney nickel activated catalyst (supplied as a 50% slurry in water, pH 10 by Aldrich Chemical Company) was washed twice with ethanol (150 ml) and added to a solution of 15.9 g of V in 500 ml of ethanol. The mixture was stirred at room temperature for two hours. An additional 18 g of Raney nickel was added, and the mixture was stirred at room temperature for three hours. Following workup, 9.11 g (83.4%) of crude ethyl 2,6,6-trimethylcyclohex-2-ene-l-carboxylate (VII) sufficiently pure for the next step was obtained. 

Synthesis consists of (1) planning the reaction sequence with respect to the given conditions, (2) executing the optimal reaction path, (3) isolating the product and workup, and (4) improving yield and selectivity of the conversion by changing reagents and reaction conditions. The difference between chemical and electrochemical reactions lies mainly in the set of available reactions for points (1) and (2) and the equipment used in (2). These points will be addressed in Sects. 3.4-3.6. 

The workup for such reactions involves neutralization and concomitant generation of salts such as NaCl, Na2S04, and (NH4)2S04. The ehmination of such waste streams and a reduction in the dependence on the use of hazardous chemicals, such as phosgene, dimethyl sulfate, peracids, sodium azide, halogens, and HF, are primary goals in green chemistry. 

Phenylpyrimidine. On treatment of 4-phenylpyrimidine with potassium amide in liquid ammonia at 33°C for 70 hr in the presence of potassium nitrate, followed by quenching the reaction mixture by addition of ammonium chloride and workup, two products were isolated 2-amino-4-phenylpyrimidine (60%) and 6-amino-4-phenylpyrimidine (15%) (79JOC4677). When the reaction was carried out with labeled potassium amide in liquid ammonia and using the combined methodologies of chemical conversions and mass spectrometry as discussed previously (see Section II,C,l,a) it was found that in 6-amino-4-phenylpyrimidine (62/63), hardly any label was incorporated in the ring ( 5%), but that about... 

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