P- azobenzene

CHROMOGENICMATERIALS - PHOTOCHROMIC] (Vol6) p-Azobenzene-aisonatetrityro sine... 

Li and coworkers synthesized the novel IL l-butyl-3-trimethylsilylimid-azolium hexafluorophosphate and demonstrated its utility for liquid/ liquid extraction of inorganic mercury. Using o-carboxyphenyl diazoamino p-azobenzene as a chelator to form a stable neutral complex with the metal ion, the authors demonstrated selective extraction into the hydrophobic IL phase [19]. When sodium sulfide was added to the IL phase, the mercury ion was back-extracted into the aqueous layer, providing an avenue for recycling the IL. The authors report extraction and back-extraction efficiencies of 99.9 and 100.1%, respectively, for a 5.0 pg/L aqueous mercury standard. The mercury detection limit was 0.01 ng/mL in water and the method was successfully applied to detecting trace mercury in natural water samples. 

Cadion (p-nitrobenzenediazoaminobenzene-p-azobenzene) (formula 13.1) [48,49] is the basis of a very sensitive method for cadmium. In the presence of the non-ionic surfactant, Triton X-100, the absorptivity is 1.2-10 at 477 nm. Other azo reagents used are bromobenzothiazo (extraction into toluene, e = 5.8-10 ) [50] and Arsenazo III [51]. 

S. Chatterjee, A. PiUai, and V.K. Gupta. Spectrophotometric determination of mercury in environmental sample and fimgiddes based on its complex with o-carboxy phenyl diazoamino p-azobenzene. Talanta 57 461-465, 2002. 

Jones R, Tredgold R H, Hoorfar A, Allen R A and Hodge P 1985 Crystal-formation and growth in Langmuir-Blodgett multilayers of azobenzene derivatives—optical and structural studies Thin Solid Films 134 57-66... 

Tredgold R H, Allen R A and Hodge P 1987 X-ray-diffraction and optical studies of Langmuir-Blodgett films formed from azobenzene derivatives Thin Solid Films 155 343-52... 

The most noteworthy reaction of azo-compounds is their behaviour on reduction. Prolonged reduction first saturates the azo group, giving the hydrazo derivative (C NH-NH C), and then breaks the NH NH linkage, with the formation of two primary amine molecules. If method (1) has been employed to prepare the azo-compound, these two primary amines will therefore be respectively (a) the original amine from which the diazonium salt was prepared, and (6) the amino derivative of the amine or phenol with which the diazonium salt was coupled. For example, amino-azobenzene on complete reduction gives one equivalent of aniline, and one of p-phenylene diamine, NHaCeH NH benzene-azo-2-naphthoI similarly gives one equivalent of aniline and one of... 

Azoxybenzene, CeH NOiNCeHs, and Azobenzene, CeH5N NCeH5. (Method 2, p. 208.)... 

This view is supported by the fact that if diazominobenzene is dissolved in dimethylaniline in the presence of the hydrochloride of the latter, the main product is p-dimethylamino-azobenzene, CgHjN=NCgHgN(CH3)2 this is because dimethylaniline couples in the nucleus more readily than does aniline. The reaction is an electrophilic displacement of hydrogen by the diazonium ioii ... 

Dissolve 5 g. of finely-powdered diazoaminobenzene (Section IV,81) in 12-15 g. of aniline in a small flask and add 2-5 g. of finely-powdered aniline hydrochloride (1). Warm the mixture, with frequent shaking, on a water bath at 40-45° for 1 hour. Allow the reaction mixture to stand for 30 minutes. Then add 15 ml. of glacial acetic acid diluted with an equal volume of water stir or shake the mixture in order to remove the excess of anihne in the form of its soluble acetate. Allow the mixture to stand, with frequent shaking, for 15 minutes filter the amino-azobenzene at the pump, wash with a little water, and dry upon filter paper Recrystallise the crude p-amino-azobenzene (3-5 g. m.p. 120°) from 15-20 ml. of carbon tetrachloride to obtain the pure compound, m.p. 125°. Alternatively, the compound may be recrystaUised from dilute alcohol, to which a few drops of concentrated ammonia solution have been added. 

To prepare the hydrochloride, dissolve about 1 g. of the compound (which need not be perfectly dry) in about 8 ml. of alcohol. Add this solution to boiling dilute hydrochloric acid (10 ml. of the concentrated acid and 80 ml. of water). Boil for 5 minutes, filter the hot solution if necessary, and allow to cool. p-Amino-azobenzene hydrochloride separates in steel-blue crystals. Filter, wash with a little dilute hydrochloric acid, and dry. 

To recover the free base, dissolve the hydrochloride in the minimum volume of boiling alcohol, add concentrated ammonia solution dropwise until a clear solution results and the blue colour has become fight brown. Add water carefully untU a cloudiness appears, warm on a water bath untU the cloudiness just disappears, and allow to cool. Yellow crystals of p-amino-azobenzene separate on coofing. 

Frequently the recrystallized azobenzeno has m.p. 61°, which is unaffected by recrystallisation from alcohol. Upon distillation from a. 50 ml. distilling flask fitted with a short air condenser, the m.p. is raised to 67-5° and the recovery is about 90 per cent. one recrystallisation from diluted alcohol (as above) then gives perfectly pure azobenzene of m.p. 68-5°. 

Tropeolin OO, orange IV, sodium p-diphenylamino-azobenzene sulfonate, sodium 4 -anilino-azobenzene-4-sulfonate (indicator) dissolve 0.1 g in 100 mL water pH range red 1.3-3.2 yellow. 

The dominant mechanism of purification for column ciystallization of sohd-solution systems is reciystallization. The rate of mass transfer resulting from reciystallization is related to the concentrations of the solid phase and free hquid which are in intimate contac t. A model based on height-of-transfer-unit (HTU) concepts representing the composition profQe in the purification sec tion for the high-melting component of a binaiy solid-solution system has been reported by Powers et al. (in Zief and Wilcox, op. cit., p. 363) for total-reflux operation. Typical data for the purification of a solid-solution system, azobenzene-stilbene, are shown in Fig. 22-10. The column ciystallizer was operated... 

FIG. 22-10 Steady-state separation of azobenzene and stilbene in a center-fed column crystallizer with total-reflux operation. To convert centimeters to inches, multiply by 0.3937. (Zief and Wilcox, Fractional Solidification, vol. 1, Marcel Dekker, New York, 1967, p. 356.)... 

In a 500-ml. round-bottomed flask equipped with a reflux condenser and a magnetic stirrer (Note 6) are placed 150 ml. of methanol, 150 ml. of 6N hydrochloric acid, and the total yield of 4,4 -bis(acetamido)azobenzene. The mixture is heated under reflux for 1.5 hours. The reaction mixture is cooled and the violet solid collected on a Buchner funnel (Note 7). The damp product is suspended in 500 ml. of water in a 1-1. beaker equipped with a stirrer, and the mixture is slowly neutralized by the addition of 2.5N sodium hydroxide. In the course of the neutralization, the salt dissolves and the free base separates. The 4,4 -diaminoazo-benzene is collected on a Buchner funnel, washed with water, and dried under reduced pressure. The yield of yellow product, m.p. 238-241° (dec.),is ll-12g. The over-all yield from/ -amino-acetanilide is 52-56%. 

The first N-thiosulfinylamine 4-Me2NC6H4N=S=S (10.2) was obtained as a deep violet solid (/Inmx 510 nm) in low yield by the reaction of phosphorus pentasulfide with N,N-dimethyl-4-nitrosoaniline. Compound 10.2 (M.p. 113-115°C) has much higher thermal stability than the corresponding thionitrosoarenes, but it decomposes to the corresponding azobenzene and sulfur on heating to 200°C. 

---