Jan., 19501 QUANTITIES OF COPPER IN LEAD AND LEAD ALLOYS 27 Gravimetric Determination of Copper, Iron, Aluminium and Titanium with N-Benzoylphenylhydroxylamine BY SUDHIR CHANDRA SHOME* SYNoPsIs-N-benzoylphenylhydroxylamine, which can be easily prepared, and preserved indefinitely, has been used successfully for the gravimetric determination of copper, iron, aluminium and titanium. Copper, iron and aluminium can be determined by weighing the precipitate directly and the presence of appreciable amounts of other metals like beryllium, cobalt, cadmium, manganese, nickel, uranium (sexivalent) and zinc does not interfere with the procedure. The precipitation of iron is interfered with by the presence of aluminium and chromium. I t is possible to determine copper in presence of phosphoric acid, but the separation of iron and aluminium from phosphoric acid is not possible.In the determination of titanium with benzoylphen ylhydroxylamine, the precipitate should be ignited to oxide before weighing. Titanium has been separated from aluminium but iron and phosphoric acid interfere with the precipitation of the metal. IN an attempt to improve upon certain defects of cupferron, the ammonium salt of N-nitroso- phenylhydroxylamine, as an analytical reagent, a series of allied organic compounds were examined by the auth0r.l It was observed that N-benzoylphenylhydroxylamine (C,H,-N-OH) \ CO--C,H, unlike cupferron (free acid) (CGH5-N-ONHJ \ possessed the following useful properties : (i) the compound was stable towards heat, light and air and could be preserved indefinitely, (ii) it was soluble in hot water, (iii) the precipitates * Present address, Corrosion Section, Department of Metallurgy, Cambridge University.28 SUDHIR CHANDRA SHOME GRAVIMETRIC DETERMINATION OF COPPER, [Vd.75 formed with metal ions became granular on heating and (iv) the precipitates were not con- taminated with the organic reagent when formed in hot solution and therefore were directly weighable. The object of the present investigation was to study the use of this new organic reagent in the determination of copper, iron, aluminium and titanium. EXPERIMENTAL PREPARATION AND PROPERTIES OF BENZOYLPHENYLHYDROXYLAMINE- Benzoylphenylhydroxylamine was prepared by a slight modification of the method of Bamberger.2 Phenylhydroxylamine (30 g.) was dissolved in warm water (1200 ml.) and the solution was filtered.The filtrate was cooled, a little sodium hydrogen carbonate was added and benzoyl chloride (45 g.) was then added drop by drop while the phenylhydroxylamine solution was stirred vigorously. About 30g. of sodium hydrogen carbonate were added in small quantities at a time to keep the mixture faintly alkaline. The stirring was continued for 90 minutes and the resulting solid (a mixture of monobenzoyl- and dibenzoyl-phenyl- hydroxylamine) was filtered and washed with water. The solid was then triturated with 10 per cent. sodium hydrogen carbonate solution in a porcelain mortar for half an hour, filtered and washed with water. By this treatment the entrapped drops of benzoyl chloride were removed.The monobenzoyl derivative was separated from the dibenzoyl derivative by treating the white mixture with aqueous ammonia (sp.gr. 0-SS), in which only the mono- benzoyl compound dissolved. The solution was filtered and the filtrate was added to a slight excess of dilute sulphuric acid cooled with ice and salt. The monobenzoylphenyl- hydroxylamine that separated out was then filtered and further purified by recrystallisation from alcohol. ' Benzoylphenylhydroxylamine is very slightly soluble in cold water but soluble in hot water to the extent of about 0.5 per cent.; it is soluble in alcohol, benzene, ether, acetic acid and aqueous ammonia solution. The compound is stable towards heat, light and air. I t is very weakly acidic in character and no ammonium salt is formed when gaseous ammonia is passed through its solution in ether.Its melting-point is 121" to 122" C. REACTIONS WITH THE METAL IONS- Bamberger2 reported that benzoylphenylhydroxylamine gave a green precipitate with copper, and a red coloration with iron salt solutions. He did not study the reactions of the compound with the other metal ions. In the present investigation it was observed that benzoylphenylhydroxylamine formed precipitates with the following ions in weakly acidic or weakly alkaline medium: Pd", Pt"", Zr"", Pb', Hg", Hg', Ag', UO,", Ce"", Mn", Cr'**, Fe'", Fe", Cu", Al"', Ti"", Sn"", Sn", Th"", Ni", Co", Zn", Cd", VO,', WO,',' and MOO,". Copper, iron and aluminium ions were precipitated separately from hot aqueous solution by adding an alcoholic solution of the organic reagent in slight excess.The precipitates were thoroughly washed with hot water and dried at 110" C. Analysis of these pure com- plexes indicated that their compositions were as follows : CU(C,H~~O~N)~, Fe(C,,HloO,N), and Al(Cl,Hlo02N),. The copper, iron and aluminium complexes were green, red and white and their melting- (also decomposition-) points were 198" to 199" C., 187" to 188" C. and 238" to 239" C. respectively. The complexes were decomposed by moderately concentrated mineral acids. The yellow titanium complex was prepared from the cold solution and purified from excess of reagent by crystallisation from alcohol. Analysis of the titanium complex showed that it was not of any definite composition. The titanium complex was decomposed in presence of considerable amounts of mineral acids.All these metallic com- plexes were soluble in organic solvents. Copper and iron complexes were slightly soluble in 50 per cent. alcohol, whilst those of aluminium and titanium were more soluble. REAGENTS USED IN THE DETERMINATION OF THE METALS- (1) Metals to be determined-Standard solutions of copper sulphate, ferric alum, potash alum and titanium sulphate were prepared separately by the usual methods. A standard solution of copper chloride was used when copper was to be determined in presence of lead and mercury. (2) Foreign ions-In the study of the effect of different ions on the precipitation of the metals to be determined, alkali salts were used for the solutions of the anions, and chlorides, nitrates and sulphates were used for the solutions of the cations.Jan., 19501 IRON, ALUMINI WM AND TITANIUM WITH N-BENZOYLPBENYLHYDROXYLAMINE 29 (3) BenzoyZphenyZhydroxyZarnine soZzltiout-An alcoholic solution of the organic reagent was used for the precipitation of the metal ions.PH Adjustment-The pH of the solutions was usually adjusted by adding requisite quantities of 10 per cent. solution of sodium acetate and 1.08 N sulphuric acid. Glacial acetic acid was used instead of sulphuric acid when copper was determined in presence of lead and mercury. In the determination of titanium, the standard solution was first neutralised with 6 N ammonia solution and then acidified with the necessary amounts of concentrated hydrochloric acid (d. 1.15). A11 the chemicals used were of A.K.quality. DETERMINATION OF COPPER, IRON AND ALUMINIUM PROCEDURE- Take a known quantity of copper, iron or aluminium solution containing about 0.025 g. of copper, 0-015 g. of iron or 0.01 g. of aluminium and add 5 ml. of 1.08 N sulphuric acid solution (in the determination of iron in ferric alum, the addition of this acid is not necessary when the ferric alum solution contains the same amount of sulphuric acid). Dilute the solution with distilled water to about 400 ml. and heat to boiling. Dissolve benzoylphenylhydroxyl- amine (one and three-quarter times the theoretical quantity) in alcohol (15 to 20ml.), warm the solution and add to the hot solution of the metal. Add 10 ml. of 10 per cent. sodium acetate solution to raisk the pH of the solution to about 4-0.Occasionally stir the precipitate formed and heat it on the boiling water-bath for 1 to 2 hours (I hour for copper precipitate and 2 hours for iron and aluminium precipitates). Filter the precipitate on a No. 4 sintered glass crucible and keep the filtrate for subsequent pH measurement by means of a glass electrode. Wash the precipitate thoroughly with hot water and dry it at 110" C. to constant weight. Calculate the metal content on the basis that the precipitate contains 13.03 per cent. of copper, 8.064 per cent. of iron or 4.064 per cent. of aluminium. Notes-(@) Iron and aluminium precipitates tend to form hard lumps when precipitated above 70°C. and hence the precipitation is carried out at about 65°C. There should be good stirring when the flocculent precipitate is changed to the granular forh by heating on the water-bath.(b) During the precipitation of the metals, the benzoylphenylhydroxylamine solution is not allowed to fall on the sides of the beaker, otherwise the organic reagent would be deposited on the sides owing to the evaporation of alcohol and necessitate the use of a large volume of wash-water. (c) In the precipitation of aluminium, the alcohol in the final volume of solution should be not more than 5 per cent., because the aluminium complex is moderately soluble in alcohol. (d) The aluminium complex is very slightly soluble in hot water at 90" C. but is insoluble in boiling water containing a small amount of reagent. The aluminium precipitate is washed with warm water at about 45" C. RESULTS- The results of determinations of copper, iron and aluminium are shown in Table I.They indicate that these metals can be determined by weighing their complexes directly. EFFECT OF pH ON THE PRECIPITATION OF COPPER, IRON AND ALUMINIUM- The precipitation of copper, iron and aluminium was quantitative between the pH values of 3.6 to 6.0, 3.0 to 5.5 and 3.6 to 6.4 respectively. The metals were not precipitated completely when the pH of the solution was lower than these ranges and at higher pH values slightly high results were obtained. EFFECT OF FOREIGN IONS ON THE PRECIPITATION OF COPPER, IRON AND ALUMINIUM- (a) The presence of anions-Copper was determined in presence of phosphoric, arsenic and arsenious acids by means of benzoylphenylhydroxylamine. A small amount (5 ml.of 10 per cent. solution) of Rochelle salt was added to the copper solution in ordel: to prevent precipitation of copper phosphate, copper arsenate or copper arsenite when the pH of the solution was raised to about 4-6 by adding sodium acetate solution. The results are given in Table 11.30 SUDHIR CHANDRA SHOME : GRAVIMETRIC DETERMINATION OF COPPER, [Vol. 75 Attempts to separate iron and aluminium from phosphoric acid with the help of benzoyl- phenylh ydroxylamine were not successful. Copper, iron and aluminium were determined separately in presence of large amounts of tartrate ion. Benzoylphenylhydroxylamine gave precipitates with vanadate, molybdate and tungstate ions in acid medium and therefore copper, iron and aluminium could not be separated from these ions.TABLE I DETERMINATION OF COPPER, IRON AND ALUMINIUM WITH BENZOYLPHENYLHYDROXYLAMINE pH of the solution == 3.9 to 4.0 Metal taken g* 0.03156 (CU) 0.02777 97 0.02651 )) 0.02525 97 0.01728 (Fe) 0.01656 79 0.01690 35 0.01440 97 0-01021 (Al) 0.00899 ) 9 0*00817 9> 0.00817 7 9 Wt. of ppt. g. 0.2426 0.2136 0.2037 0.1935 0.2148 0.2045 0.1964 0-1780 0.2506 0.2220 0.2014 0.1999 Metal foun g. 0.03 161 0.02783 0.02655 0,02522 0-01732 0.01 649 0.01584 0.01435 0.0 101 8 0.00902 0.008 18 0.00812 Id Error g- + 0.00005 + 0.00006 + 0.00004 + 0.00004 - 0.00003 - 0.00007 - 0.00006 -0*00005 - 0.00003 + 0.00003 + 0~00001 - 0.00005 (b) TIze 9resence of catiom-Preliminary experiments revealed that cobalt, cadmium, lead, mercuryn, manganese, nickel, uraniumv1, and zinc did not form any precipitate with benzoylphenylhydroxylamine at pH 4.0.Copper, iron and aluminium were, therefore, TABLE I1 pH of the solution = 4-5 to 4.7 g. g. g. g. €5 0.02525 0.16 (P20s) 0.1930 0.02515 - 0*00010 79 0.02 n 0.1938 0.02525 0~00000 97 0.10 (Ago6) 0.1942 + 0-00005 ?9 0.10 (AqO,) 0.1943 0.02531 + 0.00006 DETERMINATION OF COPPER IN PRESENCE OF PHOSPHORIC, ARSENIC AND ARSENIOUS ACIDS Copper taken Acid added wt. of ppt. Copper found Error 0.02530 determinable in presence of the above-mentioned ions. Results are recorded in Table 111, and show that copper, iron and aluminium can be separated from many other different metal ions. Benzoylphenylhydroxylamine precipitated tin, titanium and zirconium ions in acid solution. Copper, iron and aluminium could not be determined in presence of each other or in presence of any of the three above-mentioned ions by means of this organic reagent.The precipitation of iron with benzoylphenylhydroxylamine was interfered with by the presence of chromic ion. DETERMINATION OF TITANIUM PROCEDURE- Take a known quantity of the titanium sulphate solution containing about 0.1 g. of TiO, and add distilled water to make the volume about 400ml. Neutralise the solution with ammonia solution and add 5 ml. of concentrated hydrochloric acid. Precipitate titanium by adding slowly a 10 per cent. alcoholic solution of benzoylphenylhydroxylamine (about double the theoretical quantity) to the clear solution of the metal, with constant stirring. Allow the precipitate to stand for 45 minutes with occasional stirring, filter and wash with dilute hydrochloric acid containing the organic reagent (to prepare the wash-solution, add 10ml.of benzoylphenylhydroxylamine solution to 1 litre of warm distilled water, cool and mix with 3 ml. of concentrated hydrochloric acid). Ignite the precipitate carefully in a platinum crucible to constant weight and weigh as titanium dioxide. Notes-(a) A gummy substance is formed when titanium is precipitated from a warm solution and hence the titanium solution is kept below 25" C. for precipitation.Jan., 19.501 IRON, ALUMINIUM AND TITANIUM WITH N-BENZOYLPHENYLHYDHOXYLAMINE 31 TABLE I11 DETERMINATION OF COPPER, IRON AND ALUMINIUM IN PRESENCE OF pH of the solution = 3-9 to 4.1 FOREIGN METAL IONS Metal taken g. 0.02967 (CU) 0.02525 99 99 99 99 99 99 tt 99 97 0.03156 97 99 9) 79 99 0.01440 (Fe) 99 99 99 9Y 99 99 97 99 0.00817 (Al) 99 99 93 9s Y Y t? 99 77 99 79 Foreign metal added €5 0.08 (Pb) ” (Hg) 0.01 (Be) 0.12 (CO) 0.16 (Cd) 0.08 (Zn) 0.06 (Mn) 0-12 (Ni) 0.16 (U) 0.14 (CO) 0.17 (Ni) 0.28 (Mn) 0.24 (U) 0.12 (Zn) 0.02 (Be) 39 (Ni) 3% (Mn) $9 (Zn) 99 (Co) ” (U) Wt.of ppt. g. 0.2280 0.2271 0.1939 0.1930 0.1939 0.1944 0.2427 0.2434 0.2421 0.1791 0.1784 0.1 783 0.177% 0,1793 0.2008 0.2000 0.1999 0.20 18 0*2000 0.2004 Metal found g. 0-02970 0.02959 0.02526 0.02515 0.02526 0.02533 0-03161 0.0317 1 0.03154 0.01444 0.01438 0.0 143 7 0.01434 0.01445 0*00816 0.00813 0.00812 0.00820 0.00813 0.008 14 Error €5 + 0*00003 - 0.00008 + 0~00001 - 0*00010 + 0~00001 + 0-00008 + 0*00005 + 0.000 16 - 0~00002 + 0.00004 - 0~00002 - 0.00003 - 0.00006 + 0.00006 - 0~00001 - 0.90004 - 0.00005 - 0.00004 - 0.00003 + 0*00003 (b) The titanium precipitate is moderately soluble in alcohol and therefore the alcohol in the final solution should not be more than 5 per cent.RESULTS- It was found that this determination was possible when concentrated hydrochloric acid up to 20 ml. was added; the precipitation of titanium was incomplete if more acid was used. The results of the determination of titanium are shown in Table IV. TABLE IV DETERMINATION OF TITANIUM WITH BENZOYLPHENYLHYDROXYLAMINE Titanium dioxide Titanium dioxide taken found Error g* g. g. 0.1082 0.1081 - 0*0001 0-0773 0.077 1 - 0~0002 0.0742 0.0744 + 0.0002 0.0618 0.0616 - 0.0002 0.0464 0.0460 - 0.0004 EFFECT OF FOREIGN IONS- Table V.was determined in presence of large amounts of tartrate ion. from iron or phosphate ion was not possible. Results of determinations of titanium in presence of aluminium ion are recorded in The metal The separation of titanium It is seen that titanium can be determined in presence of aluminium. TABLE V DETERMINATION OF TITANIUM IN THE PRESENCE OF ALUMINIUM Titanium dioxide taken g. 0.1082 0-1082 0.0773 0.0433 0.0402 Aluminium sesquioxide added g- 0.10 0.05 0.10 0-05 0.10 Titanium dioxide found Error g - €5 0.1084 + 0~0002 0.1079 -0.0003 0.0770 - 0.0003 0-0432 - 0.000 1 0.0400 - 0.000232 BLAKE : APPLICATION OF RADIO-FREQUENCIES TO CONDUCTIMETRIC [VOl. 75 DISCUSSION The essential difference between benzoylphenylhydroxylamine and cupferron is that there is a benzoyl group in the molecule of the former instead of the nitroso group of the latter.Owing to this difference benzoylphenylhydroxylamine has some properties (e.g. , stability and solubility in water) better than those of the free acid of cupferron. In the determination of copper, iron and aluminium with this new organic reagent, the precipitate can be weighed directly, which is a distinct advantage over the cupferron method in which the precipitate should be ignited to oxide before weighing. Small quantities of the metals can be determined more accurately with benzoylphenylhydroxylamine since the weight of the metal complex produced from a given amount of metal is nine to thirteen times greater than the weight of the corresponding oxide. Some of th? metal ions such as lead and mercury, which interfere with the determination of copper by the cupferron method, have no influence when benzoylphenylhydroxylamine is employed. The results obtained by this new method are accurate. Moreover the organic reagent can be prepared easily and preserved indefinitely. The acidity of benzoylphenylhydroxylamine is less than that of nitrosophenylhydroxyl- amine (free acid of cupferron) and therefore, its complexes with the metal ions are more easily decomposed by mineral acids. Owing to this defect, iron cannot be precipitated in strong acid solution and the separation of the metal from aluminium, chromium or phosphoric acid, is not possible. In such circumstances and in the separation of titanium from phosphoric acid, the use of cupferron is preferred. The author wishes to express his gratitude to Sir J. C. Ghosh, Kt., D.Sc., F.N.I., Director, Indian Institute of Science, for the opportunities afforded to him for carrying out this investiga- tion and for advice and encouragement. His thanks are also due to Dr. S. C. Bhattacharyya for his valuable suggestions and help. REFERENCES 1. 2. Shome, S. C., Current Sci., 1944, 13, 257. Bamberger, E., Ber., 1919, 52, 1116. DEPARTMENT OF CHEMISTRY BANGALORE, INDIA INDIAN INSTITUTE OF SCIENCE Februavy, 1949