Recrystallization Resonance

Proton magnetic resonance (CDC13) 8, number of protons, multiplicity, coupling constant J in Hz. 1.5-2.2 (2, multiple ), 2.7-3.0 (4, multiplct), 7.0 (1, doublet, J = 2.5), 7.1-7.5 (6, multiplet), 7.7-8.2 (4, multiplet). A sample recrystallized from methanol-chloroform melted at 183-185°. The submitters also obtained pure product, m.p. 181-183°, after chromatography on basic alumina with 20% petroleum ether in dichloromethane as eluent. 

The proton magnetic resonance spectrum (benzene-d6) indicated the presence of less than 5% p-benzoquinone. This material darkens upon standing even in a refrigerator recrystallization should be performed as soon as possible. 

The a-plienylcinnamonitrile (Note 4) present in the distillation flask can be recovered. The residue is broken up with 75 ml. of methanol, the mixture stirred and cooled, and the product recovered by filtration. Recrystallization from methanol gives 17-20 g. of crystalline material, m.p. 86-88°. The proton magnetic resonance spectrum (chloroform-d) shows complex multiplets at 5 7.20-8.00. 

The checkers obtained 12.8-13.0 g. (52-53%), m.p. 84-86°, in the first crop and 2.7-3.4 g. (11-14%), m.p. 52-62°, in the second crop. Recrystallization of the former from methanol gave 11.5 g. of crystals, m.p. 84-86°, suggesting that the first crop is a pure single isomer. A proton magnetic resonance spectrum in chloroform-d of the second crop shows two singlets at 8 1.62 and 1.64 for the terf-butyl groups. Thus this material is a mixture of syn and anti isomers. Both the first and second crops proved equally useful for tcrf-butoxycarbonylation of an amino acid. 

The submitters obtained 59.6-64.1 g. (65-70%) of product melting at 36-37° after recrystallization from ethanol. Reported melting points for bis(phenylthio)methane are 34-35°, 38-40°, and 39.5-40.5°." The proton magnetic resonance spectrum of the product in carbon tetrachloride exhibits a two-proton singlet at 8 4.30 and a 10-proton multiplet at 8 7.10-7.56. 

Diphenoxy-2-propanol (3) was prepared from phenol and epichlorohydrin (l-chloro-2,3-epoxypropane), as previously described,8 and recrystallized three times from 2-propanol to yield white crystals, m.p. 82-82.5°C. The nmr spectrum in CDC1- (Varian EM-390 spectrometer) exhibited resonances (in ppm (6) relative to tetramethylsilane) at 3.0 (1H, doublet,... 

In principle, separation of resonances of diastereomeric compounds (such as dl and meso isomers) may be increased simply through use of an appropriate achiral solvent. Chiral solvents may in some cases be especially effective in producing a separation, particularly if the diastereomers differ in configuration about a center that is amenable to analysis by the CSA method. Kaehler and Rehse (89) give a detailed account of conditions necessary for measurement of the ratio of meso- and dZ-tartaric acid employing A,N-dimethyl PEA. Bomyl acetate used as solvent for l,2-difluoro-l,2-dichloroethane (90) allows measurement of the diastereomeric composition. Paquette and co-workers (91,92), using TFAE, were able to determine the diastereomeric purity of the recrystallized adducts 47 of... 

The condensation products were purified by rectification and, when possible, by subsequent recrystallization. Through gas chromatographic analysis the purity of asym DAMs was found to be 99% +. The structures of these compounds have been identified by elemental analysis, infrared, nuclear magnetic resonance, and mass spectra (50, 51). The properties of the asym DAMs which we prepared are listed in Table I 42). 

D. Kawase et al. investigated Si regrowth from the amorphous phase caused by Al implantation recrystallization of the specimens when annealed at temperatures between 800-1,600°C in Ar flow for 30 minutes was achieved [78]. The damage induced by the implantation and the damage reductions by the subsequent annealing were determined by electron spin resonance (ESR) and TEM. 

Di-p-chloro-bis(i74-l,5-cyclooctadiene)dirhodium(I) is a yellow-orange, air-stable solid. It can be used directly as obtained for preparative purposes5 or as a precursor for homogeneous catalysts.3,4 It can be recrystallized from dichloro-methane-diethyl ether to give orange prisms. The compound is soluble in dichloro-methane somewhat less soluble in acetone and insoluble in pentane and diethyl ether. Characteristic strong bands occur in the infrared spectrum at 819, 964, and 998 cm 1 (Nujol mull). The cyclooctadiene vinylic protons resonate in the 1H NMR spectrum at t 5.7 and the allylic protons at t 7.4-8.3 (deuteriochloroform solution). Other physical properties are given by Chatt.1... 

The material is normally utilized directly without further purification. If the solid is very gray, it may be recrystallized. For the recrystallization the salt is dissolved in hot 95% ethanol (approximately 350 ml. per 100 g. of salt) containing decolorizing carbon, filtered rapidly, and the clear supernatant liquid is allowed to cool in a freezer (—20°). In this way, white crystals, m.p. 106-107°, may be obtained with nearly quantitative recovery. The checkers obtained the purified material of m.p. 108-109° with 95% recovery and used this material for the next step. The purified material has the following spectral data ultraviolet (95% ethanol) nm. max (e) 236 shoulder (13,200), 262 (2200), 268 (2680), 275 (1010) infrared (Nujol) cm-1 3090 weak, 3060 weak (aromatic CH), 1580 weak (C=C) proton magnetic resonance (CDCla), first-order analysis, 6 in p.p.m. 7.5-8.2 (multiplet 10H, Ha), 4.3 (poorly resolved triplet 2H, Hb), 3.75 (triplet 2H, Hd), 2-2.5 (multiplet 2H, He) coupling constant J in Hz. Jbc — 8, Jcd = 6.5. 

The checkers recrystallized the product from petroleum ether (dissolved at room temperature and cooled to -20°) and obtained a pure product of m.p. 45-46° (88.5% recovery). The pure product has the following spectral data infrared (chloroform) cm-1 1712 (0=0) proton magnetic resonance (chloroform-d) 8 (multiplicity, number of protons, assignment) 0.93 [singlet, 9, C(CH3)3], 1.3-2.2 (multiplet, 5,CH2—CH—CH2), and 2.2-2.50 (multiplet, 4, CH2— CO—CH2). 

The solidified residue is homogeneous by gas chromatography, and its infrared and nuclear magnetic resonance spectra and gas chromatogram are identical to those of recrystallized authentic benzyl sulfide. The product may be recrystallized in ca. 25 ml. of absolute ethanol to yield colorless plates, m.p. 47-48° (literature3 m p 50°), which give a satisfactory combustion analysis... 

The 31P NMR of the Li+ salt (see Properties under Section A for details of this NMR sample preparation) gives a single P(2) resonance at 8 — 22.6 ppm for the product recrystallized twice from water. If the crude material is recrystallized only once an unassigned resonance (<5%) is observed at 8 — 34.0 ppm. (Note the importance of the recrystallization step(s) prior to... 

Creatinine 2(1 mmol) and solid aldehyde 1 (1.5 mmol) were crushed with a mortar and pestle. The mixture was irradiated in an open Pyrex tube 8 mm diameter with forcussed microwaves (40 W or 60 W) in resonance cavity TE01 at 2450 MHz with a universal generator MES 73-800, previously described. The mixture was washed with water and then with ether to remove excess aldehyde. Recrystallization from alcohol yielded the condensation product. 

Variable temperature (-150° to +350°) chemical shift spectra have been obtained for melt-recrystallized samples of PTFE. The NMR spectra were acquired using the REV-8 sequence which consists of a long train of closely spaced, high power rf pulses of fixed width, and varying in phase in a cyclical fashion. The cycle consists of eight ir/2 pulses. The total cycle time used was 43.2 psec with a shortest spacing between pulses of 3.6 usee. The nominal resonance frequency was 84.6... 

The (S)-(-)-isomer (lb) was the one required for synthesis of the herbicides. Reaction of racemic 2-chloropropionic acid with one equivalent of (//)-(+)-a-phenylethylaminc (2) gave a quantitative yield of the mixture of diastereoisomeric salts, which after 4 recrystallizations gave the required diastereoisomer in 20% yield [i.e., 40% based on the (S)-(-)-isomer present] with a de of 88% (determined by nuclear magnetic resonance, or NMR). The free acid (lb) was obtained quantitatively and without racemization on acidification of the salt, and the (R)-(+)-a-phenylethylamine was also recovered without racemization in 89% yield. 

Whilst this chapter is not comprehensive, attention is focused on those reports of photooxygenation where peroxide yields approached or exceeded 50%. The isolation of peroxides involves meticulous and potentially dangerous work [1]. Thus, percentage yields are not always reported in the same way, and may relate to the feasibility of purification and safety and, perhaps because of this issue, safety information is often incomplete. Analytical methods such as low-temperature nuclear magnetic resonance (NMR) spectroscopy has allowed the characterization of unstable peroxides in reaction mixtures. Some peroxides have been isolated in traps under vacuum or by low-temperature silica gel chromatography, while others were recrystallized at room temperature [2—4]. 

The yellow complex decomposes at 210°C. Upon recrystallization from dichloromethane the monosolvate is formed which melts at 185°C. In solution the complex exhibits fluxional behavior. The high field H NMR spectrum shows the hydride resonance to be composed of a quintet of doublets centered at r w 28.4. In benzene solution [x]p = — 3.4°.218... 

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