IRON AND CERIC11 COMPOUKDS AND INSULIK AS INDUCTORS 1 3 OXIDATIOX REACTIONS AXD T H E MECHANISM O F INDUCED REACTIOXS BY X. R. DHAR
Iron and Cerium Compounds a s Inductors and the Mechanism of Induced Oxidations I n several publications the author' has emphasised the aide applicability of induced reactions and numerous reducing agents have been used as inductors. But ferrous and cerous salts and sodium sulphite are the inductors, which have been largely investigated. Numerous organic compounds and several food materials, nickelous hydroxide, sodium arsenite, etc., have been oxidised simply by passing air a t the ordinary temperature through solutions or suspensions of the substances in contact with freshly precipitated ferrous hydroxide, which plays the part of a n inductor. Similar results have been obtained with cerous hydroxide and sodium sulphite as inductors. Goard and Ridea12 have oxidised several sugars and potassium arsenite in the presence cerous hydroxide. Spoeh? has oxidised sugars, glycerol etc., by passing air through solutions of the substances containing an excess of sodium pyrophosphate and ferrous or ferric salt. I n those cases, where the inductor is sparingly soluble, the oxidation is more rapid, because of the surface of the inductor. Spoehr as well as Dhar and coworkers have found that ferrous salts are more active than ferric salts, as these induced oxidations are caused by the simultaneous oxidation of the ferrous salts. I n order to explain the mechanism of these induced oxidations in the presence of ferrous and cerous salts, the formation of higher oxides like FeOz (Manchot4) and C e 2 0 j (Job5) has been assumed; and these higher oxides oxidise the difficultly oxidisable substances like the food materials. In the oxidation of organic substances by hydrogen peroxide and ferrous salts, the formation of the oxides FelOr (Manchot6) and FeOa (Hale') has been assumed. The experimental results of Palit and DhaP on the oxidation of sodium formate by air in the presence of ferrous and cerous hydroxides lend support to the hypothesis of the intermediate formation of the higher oxides 1 Dhar: J. Chem. Soc. 111, 697 (1917); Proc. Akad. Wet. Amsterdam, 29, 1023 (1921); Mittra and Dhar: Z. anorg. Chem., 122,146 (1922); ,J. Phys. Chem., 29,376; Palit and Dhar: 799 (1925); 30,939 (1926); 32, I663 (1928); 34, 711 (1930). Proc. Roy. Soc., 105A, 148 (1924). J. Am. Chern. Soc., 46, 1494 (1924). Ann., 314, 177 (1899); 325,93 (1902); 460, 179 (1927). 5 Job: Ann. Chim. Phys., (7) 20, 207 (1900). 5 loc. tit. 7 J. Phys. Chem., 33, 1633 (1929). 8 J. Phys. Chem., 34, 711 (1930).
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FezOsand Cez05. This hypothesis of the formation of higher oxides is based on the determinations of the induction factor; but Dhar and coworkers and Hale have shown that the induction factor changes with the concentrations of the inductor and the acceptor as well as with the pH value of the medium.' Goard and Rideal and Manchot have utilised the oxidation-reduction potentials in determining the true nature of the intermediate peroxide compounds. But these results have to be accepted with a good deal of caution, in view of the results obtained by Ihle,2 who found that the potential of nitric acid is lowered by the addition of a trace of nitrous acid, although this treatment increases the oxidative activity of nitric acid. Dhara has given out the view that the primary reaction in all induced oxidations consists in the oxidation of the inductor, and that this is exothermic e.g. oxidation of phosphorus, sodium sulphite, ferrous salt, etc. The energy of this exothermal chemical change may be partly given out in the form of ions and electrons, which will activate the molecules of the acceptor or actor or both and thus the induced reaction takes place. Dhal.' has shown that by passing air through water in which a mixture of phosphorus and sulphur is suspended, considerable amount of sulphuric acid is formed; and it is well known that ions are generated in the oxidation of phosphorus. This hypothesis easily explains the observed variation of the induction factor, under different experimental conditions, whereas according to the peroxide hypothesis, the induction factor should have a definite unchangeable value. With changing experimental conditions, the ions generated in the primary reaction may be dissipated before they can activate the molecules of the acceptor or the actor. Mittra and D h a r found that increasing the concentration of the acceptor (sodium arsenite) while keeping the concentration of the inductor the same (sodium sulphite) increases the inductor factor. Similar results are obtained by Dha$ in the induced reaction between oxalic acid and mercuric chloride in presence of potassium permanganate as inductor. These results can be explained as follows:Ions are generated in the primary exothermal oxidation of the inductor; these ions have a greater chance of being dissipated in dilute solutions of the acceptor than in the stronger solutions. From the experimental results of Palit and Dhar on the induced oxidation of glucose by air in presence of ferrous and cerous hydroxides, it will be seen that the induction factor (i.e.) the ratio of the amount of oxygen taken up by glucose to the amount of oxygen taken up by the inductor is as high as 8 or 9. Similar results are obtained by the above authors with other reactions. From Spoehr's results on the induced oxidation of glucose by air in presence of sodium ferropyrophosphate, it will be seen that induction factor has a value 15. It 1
Compare Gire: Compt. rend., 171, 174 (1920) and Spoehr: loc. cit.
* 2. physik. Chem., 19, 577 (1896). 3
6
J. Phys. Chem., 28, 948 (1924); 2. anorg. Chem., 159, 2. anorg. Chem., 146, 307 (1925). J. Phys. Chem., 29, 376 (1925). J. Chem. Soc., 111, 697 (1917).
103 (1926).
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thereforeappears that the oxidised form of the inductor (Fe2030rCeOn, etc.) is also capable of oxidising the acceptor, thereby regenerating the original inductor. Hence these induced reactions appear to be partly catalytic in nature, but in as much as the rate a t which the original inductor is regenerated is small compared with the rate of its oxidation, these reactions belong more to the induced type rather than the catalytic one. Moreover Palit and Dhar have shown by analysis that the residual cerium oxide is mostly C e 0 2 in the induced oxidation of carbohydrates by air in presence of cerous hydroxide. These high values of the induction factors can be satisfactorily explained from the point of view of the generation of ions in the primary exothermal reaction. Suppose a small quantity of the inductor is oxidised; some ions will be generated in this exothermal reaction, and the ions will activate some molecules of the acceptor or the actor or both. These then react. This reaction being exothermal will, in its turn, give rise to more ions, which will activate some more molecules of the reactants and so on. Thus the oxidation of a small quantity of the inductor brings about the oxidation of a large quantity of the acceptor. This appears to be a sort of chain reaction. In a subsequent communication the mechanism of other induced reactions will be considered. Recently Chakrabarti and Dhar' have shown that when not only fats, but carbohydrates and nitrogenous substances are oxidised with hydrogen peroxide and a ferric salt a t 3 7 O , volatile aldehydic or ketonic products are formed. I n this connection it must be emphasised that the oxidising power of hydrogen peroxide is greatly increased not only by ferrous salts but by ferric salts as well. Palit and Dhar,* however, have conclusively proved in a systematic manner that fats, carbohydrates, nitrogenous and other organic substances can be completely oxidised into their main products, carbon dioxide and water by air with the help of an inductor (ferrous or cerous hydroxide) or in presence of light a t the ordinary temperature and we have thus been able to imitate successfully the physiological processes of oxidation on which animal life depends. It appears, therefore, that the intermediate iron peroxide obtained in the case of hydrogen peroxide and ferric or ferrous salts must be different from that formed with ferrous compounds and oxygen, because the products of oxidation are different in the two cases.
Body Fluids as Indicators in Biological Oxidations Some years ago in a publicationa from this laboratory it was suggested that insulin and allied substances are good reducing agents and are readily oxidised by atmospheric oxygen and the oxidation of these substances induces the oxidation of sugar in the body. We have now been able to substantiate this view by oxidation experiments on insulin and glucose. A definite volume J. Indian Chem. Soc., 6, 6 1 7 ( 1 9 2 9 ) .
* J. Phys. Chem., 34, 711 (1930). 3
Mittra and Dhar: J. Phys. Chem., 29, 376 (1925).
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of air freed from carbon dioxide was passed through an aqueous solution of insulin (British Drug House) kept a t 2 j oand the amount of carbon dioxide obtained by the oxidation of insulin was absorbed by a standard barium hydroxide solution. When glucose is added to the insulin solution and the same volume of air is passed throu'gh the mixture, glucose is slowly oxidised and this can be shown by estimation of the glucose by Fehling's solution, which, however, cannot be reduced by the insulin used in our experiments. It was shown by the author' in 192 I that the addition of sodium arsenite, which can be oxidised by air only in presence of sodium sulphite, to sodium sulphite leads to a marked retardation in the velocity of the oxidation of sodium sulphite by air. Similar results are obtained with other cases of negative catalysis in oxidation reactions, where the negative catalysis is due to the induced oxidation of the retarder, which acts an acceptor. In the experiments with insulin and glucose the oxidation of insulin, which seems to be readily oxidised by air a t the ordinary temperature, leads to the oxidation of glucose by air. In this case, the acceptor glucose acts as a negative catalyst in the oxidation of insulin by air and although the glucose itself is undergoing oxidation to carbon dioxide along with insulin, the amount of carbon dioxide formed in a unit of time is less than the amount formed from the insulin solution in absence of glucose, because the velocity of the oxidation of insulin by air is greatly retarded by the addition of glucose, which, however, is slowly oxidised by air a t the ordinary temperature in presence of insulin. Experimental results show that the addition of disodium hydrogen phosphate leads to an increase in the induced oxidation of glucose by air in presence of insulin. In several publications, the author has emphasised the importance of induced oxidations in understanding the phenomenon of animal metabolism. It has been stated that the readily oxidisable substances like glutathione and other substances present in muscle and in other parts of the body, are first oxidised by the inhaled oxygen and these Oxidations induce the oxidation of food materials. Insulin and other internal secretions also appear to be readily oxidised in the body and these lead to the oxidation of carbohydrates, fats and proteins. It is now well known that in the treatment of acute diabetes, repeated doses of insulin have to be injected in order to obtain satisfactory results. Our experiments on the oxidation of insulin by air show that it is used up by oxidation in the body and thus repeated doses are necessary. Moreover, this oxidation of insulin leads to the oxidation of glucose in the body and this explains the decrease of glucose in the diabetic blood and urine on injection of insulin. It is interesting to note that biochemists are coming to the view that plant and animal peroxidases also act like inductors in oxidation reactions. From quantitative experiments on the oxidation of carbohydrates, glycerol, proteins and fats by air in presence of freshly precipitated ferrous and cerous hydroxides and sodium sulphite as inductors, Palit and Dhar? have shown Dhar: Proc. Akad. Wet. Amsterdam, 29, 1023 (1921). J. Phys. Chem., 34, 7 1 1 (1930); Z. anorg. allgem. Chem., 191, IjO (1930)
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that the amount of carbon dioxide obtained in these slow oxidations is practically the same as is expected from the point of view that the carbohydrates, glycerol, fats and nitogenous substances are completely oxidised into carbon dioxide and water by passing air a t the ordinary temperature.’ Similarly Spoehr2 has obtained considerable amounts of carbon dioxide from the induced oxidation of carbohydrates by air in presence of sodium ferrous and ferric pyrophosphate. I am of the opinion that these results are of importance, because these oxidations are of the same type as those taking place in the animal body. Dakin? has shown that ammonium butyrate on being oxidised with hydrogen peroxide and a ferrous salt, forms acetone, acetoacetic acid, acetaldehyde etc. Chakrabarti and Dhar have shown that volatile aldehydic or ketonic products are formed when carbohydrates, fats and nitrogenous substances are oxidised with hydrogen peroxide and a ferric salt a t 37’. The author has emphasized that in normal health the food materials taken in the body are completely oxidised into carbon dioxide and water without the formation intermediate compounds, just as food materials are oxidised completely to carbon dioxide and water, when air is passed through their solutions or suspensions in presence of inductors. Intermediate compounds are only formed in the diseased condition of the animal body.3
Summary
(I) From the experimental results on the induced oxidation of sodium formate by air at the ordinary temperature in presence of ferrous and cerous hydroxides, it appears that Fe,O, and Ce205 are formed as intermediate peroxides. (2) The induction factor, that is, the ratio of the amount of oxygen taken up by glucose to the amount of oxygen absorbed by ferrous or cerous hydroxide is as high as 8 or 9. Similar results have been obtained with other carbohydratee. The induction factor in the oxidation of glucose by air in presence of sodium ferropyrophosphate is about I j. (3) These high values of the inducbion factor and its increase with the concentration of the acceptor can be satisfactorily explained from the view point of the generation of ions in the primary exothermal reaction. The ions activate the molecules of the acceptor or the actor and a sort of reaction chain is set up. (4) It has been observed that volatile aldehydic or ketonic products are formed when carbohydrates, fats and nitrogenous substances are oxidized by hydrogen peroxide and an iron salt a t 3 7 O , whilst carbon dioxide and water are obtained and there is complete oxidation when the above substances are oxidized by air in presence of ferrous hydroxide as inductor. I t appears, therefore, that the intermediate iron peroxide obtained in the case of hydrogen J. Am. Chem. Soc., 46, 1494 (1924). J. Biol. Chern., 4, 7 7 (1908). Compare Dhar: ‘,Kea. Conceptions in Biochemistry” (1931).
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peroxide and an iron compound must be different from that formed with ferrous compounds and oxygen, because the products of oxidation are different in the two cases. ( 5 ) Insulin can be readily oxidized and carbon dioxide obtained by passing air at the ordinary temperature through an aqueous solution of insulin. When glucose solution is added to it, the glucose is oxidized to carbon dioxide and this is a case of induced oxidation. The velocity of the oxidation of insulin by air is retarded by glucose, which undergoes oxidation by air at the ordinary temperature in presence of insulin acting as an inductor. These results explain the decrease of sugar in diabetic blood and urine by the injection of insulin. Addition of phosphate increases the induced oxidation of glucose in presence of insulin. It appears that in normal health, the food materials are completely oxidized to carbon dioxide and water. Intermediate compounds are formed in the diseased condition of the animal body. Chemacnl Laboratory, Allahabad Unzverszty, AUahabad, Indaa, January 29,1929.
