N-Benzoyl-JV-phenylhydroxylamine C6H5CON(OH)C6H5, as a 1 per cent solution in ethanol, precipitates a complex (C13H11O2N)2SnCl2, m.p. 171 °C, from tin(IV) solutions containing 1-8 per cent concentrated hydrochloric acid: the complex can be dried at 110°C. Apparently the reagent reduces tin(IV) to tin(II) and then forms the addition compound. Copper can be quantitatively precipitated by the reagent at pH 3.6-6.0; no interference is encountered from copper, lead, or zinc in precipitating tin from, for example, brass solutions containing 7 per cent by volume of concentrated hydrochloric acid.
JV-Benzoyl-./V-phenylhydroxylamine is a white crystalline solid, m.p. 121 °C:
* Thallium and its compounds are toxic and cause irritation to eyes and the skin: contact and inhalation should be avoided.
its solubility in water is 0.04 g per 100 mL at 25 °C and 0.5 g per 100 mL at about 80 °C.
The reagent has been used for the determination of copper, iron, and aluminium. The pH ranges for quantitative precipitation are: Cu, 3.6-6.0; Fe, 3.0-5.5; and Al, 3.6-6.4. Incomplete precipitation occurs at a lower pH, and high results are obtained at higher pH values. Titanium must be precipitated below 25 °C and ignited to, and weighed as, the dioxide. Zirconium is also precipitated. Iron and aluminium cannot be precipitated in the presence of phosphate; chromium (III) interferes with the precipitation of iron(III). The following elements do not give precipitates with the reagent at pH 4: bismuth, cadmium, cobalt, manganese, nickel, uranium(IV), and zinc.
To the sample solution of tin(IV) chloride (containing 5-20mg of tin), add 10 mL concentrated hydrochloric acid and dilute to ca 600 mL with distilled water. Add from a separatory funnel, dropwise and with constant stirring, 5 mL of a 1 per cent solution of the reagent in ethanol for each 10 mg of tin present plus 8 mL in excess. Cool in an ice bath for 4 hours, filter on a filtering crucible (sintered-glass or porcelain), wash with a few millilitres of ice water, and dry at 110 °C. Weigh as (C13HnO2N)2SnCl2.