541.12 : 547.5

THE ACTIVATION OF OXYGEN (ESPECIALLY DURING THE OXIDATION OF ALDEHYDES)

BY

W. P. JORISSEN AND P. A. A. VAN DER BEEK.

In a recent communication I ) on the oxidation of benzaldehyde with the formation of perbenzoic acid (benzoyl hydroperoxide), we have pointed out the ways in which various researchers have attempted to explain the phenomena of oxygen activation observed during the oxidation of benzaldehyde. W e confined ourselves to benzaldehyde, as this aldehyde has been the most completely investigated, although Schonbein z , has noted the activation of oxygen during the oxidation of acetaldehyde and valeraldehyde, and Jorissen has quantitatively investigated the phenomena with propionaldehyde ').

That acetaldehyde and propionaldehyde can give peracids on oxidation is evident from a patent of the Consortium fur elektro- chemischa Industrie of Niirnberg '). From this patent it appears that manganese compounds and water have a detrimental influence on the formation of the peracids, whilst low temperatures (e.g. -20') and radiation (such as that from a quartz lamp), as well as the presence of small quantities of chromium, cobalt, iron, uranium and vanadium compounds favour their formation.

The same patent also mentions that peracetic and perpropionic acids rapidly react with the corresponding aldehydes at ordinary temperatures to form acetic and propionic acids respectively.

Bodenstein ') suggested, perhaps in connection with this. that CH,CHO . 0, was an intermediate product in the formation of acetic acid from acetaldehyde.

Kiss and Demeny 'j), from their experiments carried out in the Inorganic Chemical Laboratory at Leiden on the velocity of oxidation of acetaldehyde, came to the conclusion that peracetic acid was the first product of the oxidation.

As peracids are produced by the oxidation of three aldehydes, .t is reasonable to expect their formation bv the oxidation of other aldehydes under favourable conditions. 1

I) Rec. trav. chim. 45, 245 (1926): see also the dissertation of P. A. A. van der Beek, Leiden, 6 July 1926.

2, J . prakt. Chem. 84. 406 (1861): 105, 226 (1868). 9 2. physik. Chem. 22. 48 (note 2). 59 (1897). 4, D. R. P. 269937 of 4 Febr. 1914 and the "Zusatz" thereto. ') 2. physik. Chem. 100, 121 (1922). ') Rec. trav. chim. 43, 221 (1924).

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A5 the above mentioned peracids have strong oxidising properties, it was natural that von Baeyer and Villiger '), in agreement with Bodlander a), should ascribe the activation of oxygen [decolourising of indigo, etc. which had been studied quantitatively by Jorissen ')I during the oxidation of benzaldehyde to the intermediate formation of benzoyl hydroperoxide (perbenzoic acid) although they were unable to obtain the so-called peroxide by the oxidation of benzal- dehyde.

Engler and Weissl>erg I , ' ) , however, supposed that, in the oxidation

of benzaldehyde, the first product was the peroxyde C,H,C~"'~O \ 0' €4

(in agreement with the view o f Bach ' I ) ) and that this substance then changed to benzoylhydroperoxide. In connection with this, Engler and Weissberg state : "Numerous experiments that we have carried out in comparing the activity of v. Baeyer's benzoylhydro- peroxide, dissolved in benzaldehyde, with equally strong active peroxide solutions prepared by the aucoxidation o f benzaldeh yde have resulted in the occurrence of: differences in the velocity and nature of deoxidation."

As we had been ahle to demonstrate the formation ofperbenzoic acid in large quantities (up to 63" 0 of the calculated) in the oxidation of benzaldehyde dissolved in acetone, Bodlander and von Baeyer's view of the nature cf the oxygen activation seemed to have been supported. Soon afterwards, however, results were obtained *j which necessitated

an alteration of this possible explanation. Besides acetone, we had found that benzene, petrol (benzine),

chloroform and carbon tetrachloride were among the solvents that stabilise the peroxide formed during the oxidation of benzaldehyde. (Benzine had been used already by Suida 12), who exposed a solution of benzaldehyde in this liquid for same days a t a temperature of -70' to --80° to the action of oxygen under the rays of a Heraeus quartz lamp. H e found small quantities of peroxide which he was unable to completely identify).

We now obtained the following phenomena with carbon tetra- chloride: An experiment carried out with a low temperature of the surroundings (but without intentional cooling) gave a good yield of peroxide: about 40 O ' O of the calculated. An experiment a t a higher

? Ber. 33, 1582 (1900). ') Ueber langsame Verbreiinung, 1819. 9 Z . physik. Chem. 22. 45, 54 (1897). "9 Krit. Studien ti. d. Voigange der Autoxydation 1904. 90.

*) T h e experiments have heen carried out with financial aid froin the "Hoogewerff-

'? Rer. 47, 471 (1914).

Compt. rend. 124. 951 :1897). Mon. sci. 1897, 479.

Fonds".

i4

temperature (but without definite warming) in strong sunlight soon gave evidence of the formation of phosgene. At the same time hydrogen chloride and carbon dioxide appeared to be present. The phosgene was identified by the smell and by the formation of urea with dry ammonia, the latter also combining with the carbon dioxide to form ammonium carbamate. On repeating the experiment with a number of 2-litre flasks filled with oxygen and each containing 50 C.C. of carbon tetrachloride and 5 C.C. of benzaldehyde, thesame result was obtained. In sunlight a strong phosgene smell very soon appeared. The oxygen was rapidly absorbed, and the reaction mixture became yellow, and finally red in colour ; potassium iodide then no longer showed the presence of peroxide. Investigation of the residue has not yet indicated what is formed besides the above named gases, although a strong phenolic odour has been observed.

That the oxidation of the carbon tetrachloride was not due to benzoyl hydroperoxide was shown by the following experiment. A large excess of the latter substance was dissolved in carbon tetra- chloride and exposed to sunlight in an atmosophere of oxygen. After fourteen days no phosgene appeared to have been formed.

The solution was then boiled for three hours under a reflux condenser. A slight evolution of phosgene was observed, but most of the peroxide appeared to have remained unaltered.

Benzaldehyde oxidised in sunlight and in an atmosphere of oxygen thus differs from benzoyl hydroperoxide in its behaviour towards carbon tetrachloride. The impression is gathered that, at a low (at least, at a not too high) temperature, carbon tetrachloride functions chiefly as a solvent, but that at a higher temperature it behaves as an “acceptor” (as, for example, does indigo).

The phenomena of oxygen activation cannot, therefore, be completely explained by the intermediate formation of benzoyl hydro- peroxide.

In the activation of oxygen shewn by oxidising triethylphosphine, the difference of the properties of the oxidation product of this substance, and of the substance whilst it is oxidising. is still more striking.

Jorissen 1 3 ) found that, in the oxidation of triethylphosphine in the presence of an acceptor, both substances took up one atom of oxygen. In the absence of an acceptor, however, far more oxygen was taken up by triethylphosphine than corresponds to the formation of triethylphosphine oxide, and it appeared that one or more esters of phosphinic acids were formed.

Engler and Wild 14) found that triethylphosphine. in the absence of an acceptor, takes up practically one molecule of oxygen per molecule. By cooling with ice they obtained crystals which gave

In) Ber. 29, 1707 \1896), 2. physik. Chern. 22, 35 (1897). 1 4 ) Ber. 30, 1676 (1897).

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an oily-like liquid at ordinary temperatures and did not become solid again at - 1 5 O . Neither the crystals nor the liquid gave a peroxide reaction, They were of the opinion, however, that a peroxide was first formed, giving as an argument the fact that explosions occur when pure oxygen is passed without cooling through triethyl- phosphine.

Engler and Weijsberg ”), by oxidising large quantities of this substance, obtained, besides (C,H,),PO, a large amount of (C2H5),P02, which consisted chiefly of OP(C,H,),(OC,H,). At the end of the oxidation peroxide reactions were observed.

Whereas in the case 0 1 benzaldehyde and triethylphosphine the taking up of one molecule o f oxygen per molecule has been observed (in the latter case the product, however, not being a peroxide), in the case of sodium sulphite, which also shows the same quantitative phenomena of oxygen activation 1 6 ) , up to the present sodium sulphate has been found to be the only oxidation product.

These three subsrances appear to he representatives of the three different types of okygen activators.

If we wish to consider the activation of oxygen by an aldehyde, triethylphosphine arid sodium sulphite - which all show complete agreement as far as the quantity of active oxygen is concerned ,- from a single point of view, then we can suppose the formation of a very unstable pero.<ide 17) in all three cases. I n the case of the aldehyde this peroxide passes over to the stable peracid of the same oxygen content, in the case of triethylphosphine chiefly to the ethyl ester of diethylphosphinic acid also of the same oxygen content, and in the case of sod:.um sulphite to sodium sulphate containing only half the oxygen hypothetically taken up. In the presence of an acceptor it appears that benzoic acid is formed from benzaldehyde, triethylphosphine oxide from triethylphosphine, and sodium sulphate from sodium suiphi-:e, whilst the acceptor has taken up the same amount of oxygen. I”)

But can we not, in place of the hypothetical “very unstable peroxide”, suppose a “tendency” to the formation of a compound of one mol. of the autoxidisable substance (inductor) and one mol. of oxygen? A tendency which results in an alteration of the oxygen molecule such that il: reacts a t the same time with the inductor and the acceptor, and in such a manner that both take up half of the oxygen molecule. As our knowledge of the constitution of atoms and their

lb) Ber. 31. 3055 (1898). I” ) Jorissen, Z . physik. Chem. 23, 677 (1897): Jorissen and C. van den Pol, Rec.

trav. chim. 43, 582 (1924,. 44, 805 (1925). ’;) Bodlander (Ueber langsame Verbrennnng, Stuttgart, lh99, 478) and also Engler

and Weissberg (Kritische Studien uber die Vorgange der Autoxydation, Braunschweig. 1904, 60) suppose, in the case of Na2S0,, , the primary formation of the still unknown Na,SO,.

.“) Jorissen. Ber. 29, 1737 11896): Z . physik. Chem. 22, 34, 54: 23, 667 (1897).

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mutual action is still in its infancy, no more will be said at present as to the nature of this “alteration”.

We recall in this connection, however, the views of J. Boeseken ”) on catalytic action and those of H. J. Prins ”) on mutual activation.

L e i d e n, Inorganic Chemical Laboratory of the University, December 1926.

( R e p le 8 janvier 1927).

]!)I Rec. trav. chim. 29. 86 (1910). 30. 88 (1911). Verslaa. Akad. Wetenschappen .. Amsterdam 23, 291 (1914) and other papers.

2”) Chem. Weekblad 11, 789 (1914): 12, 46 (1915): 14, 67 (1917): 23, 389 (1926) and other papers.