Solvent bromide spectrum

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

Oxazolines have also been obtained from aziridines and carboxylic imidazolides via iV-acylaziridinesJ1271 Isomerization of the Af-acylaziridines can be achieved by heating with a catalytic amount of tetrabutylammonium iodide or bromide. The transformation can be carried out as a one-pot reaction in quantitative yield (solvents THF, CHC13, benzene) with a wide spectrum of substituents R (R = H, alkyl, c-C6Hi i, C6H5,3-pyridyl). 

Cycloheptatrienylium bromide, instead of having the properties of a typical covalent organic halide, melts at 203°, is strongly deliquescent, miscible with water, and insoluble in the less polar organic solvents. The infrared spectrum is a simple one consistent with the high degree of symmetry postulated for the ion. 

Normal glass will only transmit radiation between about 350 nm and 3 /rm and, as a result, its use is restricted to the visible and near infrared regions of the spectrum. Materials suitable for the ultraviolet region include quartz and fused silica (Figure 2.28). The choice of materials for use in the infrared region presents some problems and most are alkali metal halides or alkaline earth metal halides, which are soft and susceptible to attack by water, e.g. rock salt and potassium bromide. Samples are often dissolved in suitable organic solvents, e.g. carbon tetrachloride or carbon disulphide, but when this is not possible or convenient, a mixture of the solid sample with potassium bromide is prepared and pressed into a disc-shaped pellet which is placed in the light path. 

Dissolve a portion of cortisone acetate in methanol in a beaker, evaporate the solvent on a steam bath with the aid of a current air, then dry the residue at 105°C for 30 minutes. The infrared absorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP cortisone acetate RS. 

FIGURE 6. 500 MHz H-NMR partial spectra of 2-butylzinc bromide in the presence of 1 equivalent of (- -)-45, or its racemic counterpart ( )-45, at different temperatures. The side-product butane is represented by H. Methylene protons (c) are not shown in spectmm (a) due to solvent peak overlap. Assignments of the absolute configurations were made based on predicted anisotropic effects and are represented in spectrum (b). Reproduced by permission of Wiley-VCH from Reference 99... 

SYNTHESIS To a solution of 166 g bourbonal in I L MeOH there was added a solution of 66 g KOH pellets in 300 mL H,0. There was then added 120 g ethyl bromide, and the mixture was held at reflux on the steam bath for 3 h. The reaction was quenched with three volumes of H20, and made strongly basic by the addition of 25% NaOH. This was extracted with 3x300 mL CH.C1, and the pooled extracts stripped of solvent under vacuum. There remained 155 g of 3,4-diethoxybenz-aldehyde as a fluid oil that had an infra-red spectrum identical (except for being slightly wet) to that of a commercial sample from the Eastman Kodak Company. 

A solution of 10 g 2-mercapto-4-methoxyphenol in 100 mL MEK was added over the course of 1 h to a vigorously stirred suspension of 25 g finely powdered anhydrous K.CO, in 200 mL MEK that contained 14 g methylene bromide. The reflux was maintained for 48 h. After cooling, the mixture was freed of solids by filtration and the filter cake washed with 50 mL additional MEK. The combined washes and filtrate were stripped of solvent under vacuum, and the product distilled to give 3.3 g of 5-methoxy-1,3-benzoxathiol as a yellowing oil that had a bp of 110-120 °C at 1.7 mm/Hg. There was considerable residue in the pot, which was discarded. The NMR spectrum was excellent, with the methylene protons a two-hydrogen singlet at 5.6 ppm. 

The infrared spectrum of a liquid may conveniently be recorded as a thin film of the substance held in the infrared beam between two infrared-transparent discs without the need for a diluting solvent. It is customary to use polished plates of sodium chloride as the support material this material is adequately transparent in the region 2-15 /im. Spectra in the longer wavelength region (12-25 m) can be recorded using potassium bromide plates. Sealed cells (p. 267) should be used for volatile liquids. 

Cognate preparations. p-Nitrobenzaldehyde. This preparation is an example of the Sommelet reaction in which the hexaminium salt is isolated. Dissolve llg (0.13mol) of hexamethylenetetramine in 70ml of chloroform (CAUTION) and add 11.4 g (0.067 mol) of p-nitrobenzyl chloride or 14.4 g of p-nitrobenzyl bromide (Expt 6.28). Heat the mixture under reflux on a steam bath for 4 hours a precipitate gradually separates. Replace the reflux condenser by a condenser set for distillation and distil off about 35 ml of solvent. Add 35 ml of acetone, cool in ice, collect the precipitate by suction filtration and dry it in the air. Heat the hexaminium salt thus obtained under reflux for 1 hour with 100 ml of 50 per cent acetic acid then add 100 ml of water and 25 ml of concentrated hydrochloric acid and continue the refluxing for 5-10 minutes. Cool the solution in ice, collect the crystals of p-nitrobenzaldehyde and dry them in a vacuum desiccator. The yield is 6.4 g (63%), m.p. 106 °C. The p.m.r. spectrum is noted in Expt 6.117. 

Preparation of 3-hydroxy-l,3,5(10)-estratriene-17p-monobromoacetate. 10 g of l,3,5(10)-estratriene-3,17p-diol was dissolved in 400 ml of anhydrous tetrahydrofuran (THF), and then, 8.8 g of pyridine was added. A solution of 22.5 g of monobromoacetyl bromide in 74 g of carbon tetrachloride was added dropwise to the resulting solution at about -5°C to -7°C. The mixture was kept for one night. After the reaction, the resulting precipitate was separated by a filtration. The solvent was distilled off from the filtrate. The residue was dissolved in ether and recrystallized from ether to obtain l,3,5(10)-estratriene-3,17p-bis(monobromoacetate). 2 g of the product was dissolved in 900 ml of methanol and the solution was cooled to -5°C. A solution of 0.24 g of K2C03 in 20 ml of water was added dropwise to the resulting solution. After the reaction for 30 minutes, 1000 ml of water was added and the resulting precipitate was separated and dried. It was confirmed that the product was 3-hydroxy-l,3,5(10)-estradiene-17p-monobromoacetate by the elementary analysis and the IR spectrum. 

Identification The infrared absorption spectrum of a potassium bromide dispersion of sample between two sodium chloride plates exhibits relative maxima at the same wavelengths as those of a similar preparation of USP Xylitol Reference Standard. If a difference appears, dissolve portions of both the sample and the reference standard in a suitable solvent, evaporate the solutions to dryness, and repeat the test on the residues. 

In a variation of this method, the tiiin-layer adsorbent is placed in the bottom of a glass vessel togetiier with a tiiangular wick of compressed potassium bromide. Solvent is added and it rises up the wick and evaporates from the upper region. The compound is conveyed up the wick by the solvent and accumulates at the tip of the tiimgle which is then cut off, dried, and used to prepare a disk. About 10 )Xg of compound is required to produce a satisfactory spectrum. The advantage of this technique is that tiie low part of the potassiiun bromide wick acts as a filter removes finely divided adsorbent which can give rise to spurious peaks. 

Infra-red spectra can be determined in the vapour, liquid, and solid phases, but most compounds of interest to the toxicologist are solid at room temperature and the determination of spectra in this phase has been used most widely. However, it is all too easy to rush for the potassium bromide and prepare a disk, and to forget some of the problems that may arise with this technique. The advantages of determining the spectrum of a solid as a solution in a suitable solvent should not be overlooked. 

The position of the carousel is controlled automatically and only three positions are actively used. In the first position the eluent is deposited on the potassium chloride, in the second position a stream of air is drawn through the potassium chloride to remove the solvent and in the third position the spectrum is taken. The use of the carousel containing potassium chloride powder certainly increased the sensitivity of the LC/IR combination, but the finite intervals of sample collection made the system unsuitable for modern high efficiency columns. Jino and Fujimoto [30,31] employed a potassium bromide plate as a transport system. The eluent from a small bore column (flow rate 5 pi/ min)... 

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