Tungsten-iodine lamp

The photoconductivity measurements are usually performed after the dark conductivity-thermopower run. As a light source, a tungsten-iodine lamp is used with an intensity of — 50 mW cm of white light at the sample position. The results presented in this chapter refer to room temperature measurements of the photoconductivity only. The conductance under illumination (Jiu is determined 15 sec after switching on the light source and the photoconductivity Affp is calculated by subtracting the dark conductivity. 

With uranyl nitrate as a photosensitizer, vinyl chloride was polymerized at low temperatures using a tungsten-iodine lamp as the radiation source. Since this lamp produces primarily visible light, degradation of the polymer was minimized. The degree of crystallinity of the resulting polymer was said to be inversely related to the polymerization temperature [176]. 

Light-induced difference spectra were recorded using a 50 W tungsten-iodine lamp with condensor optics, cutoff filters for excitation at wavelengths >680 nm and fiber optics to illuminate the IR sample. A software-controlled shutter was used to determine illumination periods. As with redox-induced difference spectra, several dark-light-dark cycles were averaged. 

This calibration was done at the Goddard Space Flight Cnter using a setup similar to that on the satellite. The heat source is supplied by a tungsten-iodine lamp whose radiations, reflected by a concave mirror, pass through spectral filters, neutral filters, a vacuum chamber, and are finally directed onto the radiometer. 

Sources of ultraviolet radiation include (a) tungsten-filament incandescent lamps (b) tungsten-iodine cycle lamps with quartz envelopes (c) mercury-vapor lamps and (d) the zinc discharge lamp. Odier types are available, but enjoy only limited application. The hydrogen or deuterium lamps are used in the laboratory, but are delicate and costly for process uses. 

A solution of the steroid (50 mg, 0.12 mmol) in cyclohexane (10 ml) containing DIB (40 mg, 0.12 mmol) and iodine (28 mg, 0.11 mmol) was irradiated with two 100 W tungsten-filament lamps for 50 min at 40°C. The reaction mixture was poured into water and extracted with ether the organic layer was washed with aqueous sodium thiosulphate and then water, dried, concentrated and the residue was purified by column chromatography on silica gel (hexane-ethyl acetate, 9 1) to give 6/ ,19-epoxy-5a-cholestan-3/I-yl acetate (45 mg, 90%) m.p. 114-115°C. 

A solution or suspension of the acid (1 mmol) in carbon tetrachloride (75 ml) containing DIB (0.55 mmol) and iodine (0.5 mmol) was irradiated with two 100 W tungsten-filament lamps for 45 min at reflux temperature. Another portion of DIB (0.55 mmol) was then added and irradiation was continued for 45 min at reflux. The reaction mixture was washed with dilute sodium thiosulphate and water, concentrated and chromatographed (silica gel column, 9 1 hexanes-ethyl acetate) to afford the alkyl iodide. Several steroidal acids with the carboxyl group attached at a 1° or 2° carbon atom gave the corresponding iodides in good yields. Acids with a 3° a-C instead of the iodide afforded alkenes similarly, alkenes were formed with a fivefold excess of DIB in the presence of cupric acetate. Aromatic acids also underwent iododecarboxylation, in moderate yields very effective was the otherwise difficult transformation of 1,8-naphthalenedicarboxylic acid to 1,8-diiodonaphthalene (80%) [68]. Cubyl and homocubyl iodides were also prepared in excellent yield [69]. 

Quartz-iodine lamp A tungsten filament high-intensity incandescent lamp which contains iodine in a quartz envelope. Used primarily as a source of visible light. 

Tungsten-halogen lamp See quartz-iodine lamp. Other halogens may fill the lamp. 

Decomposes at 277 °C to WO2I and iodine. As a side product also WOI3 is formed. Formation of gaseous WO2I2 is considered to effect the removal of tungsten from lamp walls in halogene lamps (Chapter 7). 

Halogen lamps are timgsten lamps whose glass bulbs also contain iodine [42]. When the coil is heated incandescent volatile tungsten iodine compounds are produced in the vapor phase and these are thermally decomposed at the glowing coil. This causes a reduction in the deposition of tungsten on the surface of the... 

More recently, heating by photo-radiation with high intensity photons from quartz iodine or tungsten filament lamps has become popular. One advantage of photoradiation is that often only the substrate is heated significantly. 

A soln. of startg. alcohol in cyclohexane containing 1.7 eqs. acetoxy(hydroxy)di-phenylselenurane and 1 eq. iodine irradiated with two 100 W tungsten-filament lamps for 8 h at 55-60° - product. Y 64%. F.e. inch steroid derivs. s. R.L. Dorta et al.. Tetrahedron Letters 29, 5429-32 (1988). 

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