Isolation of the crude product

With the reaction successfully quenched, then the isolation of the crude product can be carried out, as outlined below. 

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Cognate preparation. Terephthalic acid. Use 18 g (0.169 mol) of p-xylene in place of the p-nitrotoluene and proceed as above to the stage of isolation of the crude product. Wash this with 40 ml of water followed by 20 ml of ether and purify, isolate and dry the acid as detailed above for p-nitrobenzoic acid the yield of colourless terephthalic acid is 12 g (44%) it sublimes without melting at 300 °C and is almost insoluble in water and ethanol. 

Modifications of C6 of CyD other than by tosylation are very rare. However, a single-step quantitative-yield synthesis of CyD monoaldehydes has been published. The CyD was dissolved in an organic solvent, Dess-Martin perodinane was added, and the mixture was stirred for 1 h at room temperature. Addition of acetone and cooling allowed isolation of the crude product by filtration [16]. Another synthesis was performed by using IBX (l-hydroxy-l,2-benziodoxol-3(lH)-one 1-oxide) as oxidant in DMSO. Mono-oxidation of jS-CyD was performed along with its incorporation into chitosan by a reductive coupling reaction [17]. A direct azidation of CyDs with sodium azide in the presence of triphenylphosphine-carbon tetrabromide has also been reported [18]. 

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

Yield of the crude product according to the NMR spectra. In parentheses yield of the isolated pure hydrazine. Hydrazines arc known to be prone to air oxidation and unstable upon storage or handling on silica gel. This might be the reason for the considerable loss of yield during purification. 

Following a patented procedure for the conversion of 2,4-dinitrochlorobenzene to 5-chloro-2-nitrophenol, 2,4-difluoronitrobenzene was treated with sodium hydroxide in hot aqueous dioxane containing a phase transfer catalyst. On the small scale, the reaction and isolation of 5-fluoro-2-nitrophenol, including vacuum distillation, were uneventful. On the 20 1 scale, vacuum distillation of combined batches of the crude product led to onset of decomposition at 150°C, which could not be controlled, and the residue erupted with explosive violence and a small fire ensued. Thermal examination of fresh small-scale crude material has shown that it is capable of highly exothermic decomposition, with onset of the exotherm at 150°C (ARC). It was then realised that difficulty in controlling the reaction temperature had been experienced on the 20 1 scale. It is recommended that this procedure and purification should not be attempted on so large a scale. 

Because the product and also its solutions in chloroform are so highly colored, it is difficult to judge when complete solution has been achieved. The checker, operating on a scale one-third of that reported, dissolved 13.5 g. of crude product in 180 ml. of hot chloroform, filtered the solution, and added 360 ml. of ethanol. The product did not precipitate at room temperature, but 6.1 g. of material could be isolated after the solution had been chilled. An additional 3.1 g. of product was isolated after reduction of the volume of solvent to 70 ml. The combined crops constitute the yield claimed. It is recommended that the solubility characteristics of this complex which are given in Table I (p. 48) be used as a guide for dissolution of the crude product. 

From zPr3PSeBr2 two different crystalline phases were isolated. The intended preparation from zPr3PSe with Br2 led by recrystallisation of the crude product from dichloromethane/pentane (vapour diffusion method) to monoclinic crystals (phase 1). Bromination of zPr3PSe with an excess of bromine led to a mixture of products from which a few single crystals of phase 2 were collected. 

The proton magnetic resonance spectrum of a C8De solution of the crude product exhibits benzylic CH doublets at <5 3.58 (J = 9.4 Hz., attributable to 90-96% of the threo aldol isomer) and at 8 3.42 (J = 5.3 Hz., attributable to 4-10% of the erthro aldol isomer) downfield from internal tetramethylsilane. This mixture may be separated by chromatography on acid-washed silicic acid to permit the isolation of both the threo and the erythro diastereoisomers. ... 

Interestingly, 47, 48, and 49 were isolated in 49%, 33%, and 4% yield respectively after chromatographic purification of the crude product derived from the reaction of the pro-pargylic amine 44b with two molar equivalents of BuMe2SiH, and CO (Eq. 10) [17b]. 

In 2007, Tron and Zhu reported the multicomponent synthesis of 5-iminoox-azolines (42) starting from a,a-disubstituted secondary isocyano amides (41), amines, and carbonyl components (see Fig. 15) [155]. The reaction presumably follows a similar mechanism as in the 2,4,5-trisubstituted oxazole MCR (described in Fig. 11) however, because of the absence of a-protons at the isocyano amide 41, the nonaromatized product is obtained. As in the 2,4,5-trisubstituted oxazole MCR, toluene was found to be the optimal solvent in combination with a weak Brpnsted acid. The reaction was studied for a range of aldehydes and secondary amines. In addition, a variety of functionalities such as acetate, free hydroxyl group, carbamate, and esters are tolerated. Clean conversions were observed for this MCR as indicated by NMR analysis of the crude products (isolated yield 50-68%). The... 

The reduced form of Na+, K+-ATPase inhibitor-I (10) was obtained by treatment of the protected peptide synthesized by the soln procedure with HF, followed by reaction with Hg(OAc)2. After purification of the crude product on Sephadex G-25, the reduced peptide (110 mg) was dissolved in 0.1 M NH4OAc buffer (1L, pH 7.8) at a peptide concentration of 0.018 mM and then stirred at rt. After 24 h, the major peak in the HPLC, which coeluted with the natural product, corresponded to 55% of the product distribution. The mixture was acidified to pH 3 with AcOH and 10 was purified by RP-HPLC. When the oxidation was carried out in the presence redox reagents at a peptide/GSH/GSSG ratio of 1 100 10, after 24 h the major oxidation product increased to 69%. The mixture was acidified with AcOH and the product (10) isolated by preparative HPLC yield 20%. The product was characterized by MALDI-TOF-MS and amino acid analysis a combination of enzymatic peptide mapping and synthetic approaches were applied to assign the cystine connectivities. 

Isolated yield after column chromatgraphy. Determined by NMR of the crude product. Regioselectivity was determined as i/n > 98/2. 

To a stirred solution of the step 2 product (4.12 mmol) dissolved in 20 ml THF was added a solution of the lithium salt of (2,2-dimethyl-[l,3]-dioxolan-4-yl)-methanol in 10 ml THF and the mixture refluxed for 18 hours. Upon cooling to ambient temperature, THF was partically removed and a concentrated solution/suspension of the crude product added dropwise to water. The aqueous mixture was then acidified to pH 5-6 and the precipitated polymer isolated. The polymer was redissolved in 50 ml 2 1 and then dried in vacuo at 50°C for several hours. The organic solution was extracted twice with 30 ml saturated sodium chloride solution and once with 30 ml of water. The material was dried using MgSO filtered, concentrated, and redissolved in a minimum amount of acetone and then precipitated into 100 ml hexane. Hexane was decanted, dried in vacuo, and the product isolated as a pale yellow viscous liquid in 60-90% yield. 

The pure sample is obtained by reprecipitation. Ten grams of the crude product is dissolved in 60.0 ml. of ice-cold 0.5 N hydrochloric acid with cooling in an ice bath. Then 15 ml. of ice-cold 2 N sodium hydroxide is added to the filtered solution with stirring and cooling, and m-aquabis(ethylenediamine)-hydroxocobalt(III) dithionate is isolated as above. Yield is 8.4 g. (84%). The visible absorption spectrum in acidic or basic solution of the sample reprecipitated twice in this manner does not change after the second precipitation. Anal. Found Co, 15.74 C, 12.72 ... 

The freshly ground lithium enolate 1 (1.2 equiv.) was mixed with o-anisaldehyde 2a (1 equiv.) in argon atmosphere at room temperature. The reaction was allowed to continue at room temperature under vacuum for three days, quenched with aqueous NH4CI and the mixture extracted with three portions of diethyl ether. The combined organic extract was washed with water and dried with anhydrous Na2S()4- The solvent was removed using a rotary evaporator at reduced pressure to yield the crude product. The crude product was found to contain mainly anti aldol product (syn/anti ratio 8 92). Further purification was earned out using preparative TLC with methanol-benzene (5 95 in volume) as eluent. The purified product thus isolated was a colorless solid (mp 64-65 °C, yield 70%) with the same syn/anti ratio as that of the crude product. 

Irradiation of a recrystallized sample (10-15 mg) of 1 through Pyrex in a Ray-onet carousel photoreactor (300 nm) led to clean conversion of the starting material into a single cyclobutane product over the course of 20-50 h. The original colorless crystals visibly yellowed and lost definition around the sharp edges during irradiation but did not shatter or crumble. Treatment of the crude solid reaction product with etherial diazomethane permitted isolation of the cyclobutane product 2b which was shown to have the a-truxillate-type stereochemistry. 

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