reaccion de arbuzov

8/19/2019 Reaccion de Arbuzov

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532 GARNER, CHAPIN, AX D SCANLO S VOL. 24

and the organic material was extracted with ether, dried, tiglic acid h yhi odi de intermediate melted a t 86-87.5and distilled. This isomerization yielded some angelic acid (lit.,lO 86.2-86.3'). Treatment of the hydriodidc withbut principally tiglic acid: b.p. 195-200'; m.p. 62-64' (li t., aqueous sodium carbonate at 75' yielded trans-2-butene-2-db.p. 198.5°22;m.p. 63.5-64.Ool0). in 67% yield. The product was a t least 99.5% pure accord-

trans-2-Butene-24. Tiglic acid-3-d was converted to the ing to chromatographic alfalysis. The major contaminantalkene by the method of Young, Dillon, and I~ucas.*o he was a trace of cis-2-butene-2-d.

(22) R. Fittig and H. Kopp, Ann., 195, 81 (1879). RIVERSIDE, ALIF.

[CONTRIBUTION F R O M TIIE MONSANTO CHEMICAL CO., PIASTICS D I V I S I O N ]

Mechanism of the Michaelis-Arbuzov Reaction : Olefin Formation

ALBERT Y. GARNER, EARL C. CHAPIN, A N D PATRICIA RZ SCASLON

Received Octobe, 7 1868

Support is given for the mechanism of the Michaelis-Arbuzov reaction in terms of the formation of a quwiphosphoniiim0

tsalt intermediate. T he production of olefin and &alkyl phosphonnte, (RO)ZP-H, is shown to be a general phenomenonwhen an alpha-haloslkane which has an activating group on the beta carbon is trestcd with ii trialkyl phosphite. The forrna-tion of these products is explained in terms of an intramolecular beta-climination involving the qunsiphosphonium e d t inter -mediate.

Introduction. During the preparation of diethyl6-bromoethylphosphonate (I) by the Michaelis-Arbuzov Reaction (1) using triethyl phosphite and1,2-dibromoethane (2), it was found through the

0t

R'X + (R0)a-P '-P--(OR)z + RX (1)Br-CH2-CHz-Br + C2H6O),P +

~r-CHz-CH2--P-(OC2H6)z +0

(1)

CzIIa--P-(OC2H& + CZH6Br +11) (111)

0

( I V )(CZH~O)Z--P-CH~-CH~-P--(OC~H~)? (2 )

uc.e of infrared spe ctrosco py an d vap or pha sechromatography that diethyl vinylphosphonate

(V) and diethyl phosphonate (VI) are formed.In addition, diethyl p-bromoethylphosphonate (I),diethyl ethylphosphonate (II), thyl bromide (III),and tetraethyl ethylenediphosphonate (IV) arefound as reported previously by Ford-Moore a n dW illiams' an d Kosolapoff Ib The most obvious

0 0T T

(C~~I:,O)~~P-C€I~-CH~-I -(OC~H~)z /211

0

(C&O)Z-PCH=CHz + (C2HsO)z--P-H (3)(V) ( V I )

(1) (a) A . €I. Ford-Moore and J . W. Williams, J. Chem.SOC.,1467 (1945). (b) G. M. Kosolapoff,.J. Am. Chem. Soc.,

explanation for the form ation of these produc ts isthat the tetraethyl ethylenediphosphonate (IV)decomposes under the cond itions of the rea ction.Th is decomposition, however, has been shown notto take place. The diphosphonate (IV) is s table a t211 over a period of 5 hr., an d th e initial reactionwas run at 150 to 170 .

T he following reactions were run to determine th e

gene rality of this rea ctio n as an olefin-forming0t

(CzH60)3P + Br-CH2-CHz-P-(OCPH6)z +1)

0T

C2H6-p-(0C2~I,)2 + CnH5Br +(11) (111)

0 0T

~ C ~ ~ I ~ O ~ ~ - ~ ~ - C A ~ - - C H ~ - - ~ ~ - ~ O C ~ H ~ ~ ~( IW

0 0

t( V ) ( V I )

CH2=CH--P-(OCzH~)z + €I-P-(OC,H,h (4)

0I

(CzHs0)3P + Rr-CHz--CIII-~-OC?II, +0t

C2Hs--P-( OC,H& + C&Br +0 0 01 I

(C~H~O)~-l'-CH~-C€~p-C-OCzHa + H--P-(OCz€I6)2(VII) (VI)

(11) (111)

0

+ CH-CH- eOC& + polyethyl acrylate 5 )66, 109 1944). ( V I I I )


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APRIL 1959 MICHAELIS-ARBUZOV REACTION 533

(C?H50)3P + B~-CH~-CHZ--C~HS +0t

C2H5--P-(OC2H6)2 + C2115Br +(11) (111)

0

CoH6-CII2-CII2-P-( O C Z H ~ ) ~( I X )

TI~--P-(OC~H~)Z + C~H~CH=C HZ 6 )

( V I ) ( X )

elimination reaction. In each case the productswere as written. The major products were the cx-pected Michaelis-Arbuzov products with theolefin and dialkyl phoPphonate appearing to beproducts of a less favorable side reaction. R eaction( 5 ) has been reported previously by McConnell

and Co overIza but the only products mentionedwere 111 and VII. Likewise, Abramov and Pallzbdo not report VI and VI11 as prod ucts of th is re-action. A further search of the literature yieldedseveral references3 to Michaelis-Arbuzov reactionsinvolving a-haloalkanes containing an activatinggroup on the @-carbon.Thes e autho rs report olefin,dialkyl phosphonate, or both such products.

Discussion. T he form ation of olefin and dialkylphosphonate can be explained through two mech-anisms. The first of these mechanisms involves anordinary base-catalyzed p-elimination with thetrialkyl phosphite functioning as the base. Step

(R0) jP : + X-CIIz-CH~-R’ +(RO),PH + X-CH2-CH-R’ (1)

X-CfI2-CH-R’ H2=CH--R’ + Xe (2)0

@ t

(3) involves nucleophilic att ac k by halide ion on th ealkyl carbon which is consistent with the last stepof the Michaelis-hrbuzov reaction as picturedbelow. This mechanism, however, is unlikely inview of th e relative w eakness of tria lkyl phosp hites

as bases compared with the bases usually used inp-eliminations, the high temperatures needed tomake this reaction go and the well known nueleo-philicity of phosphites.

(2) (a) R. I,. McConnell and H. W. Coover, J . Am.(“hem. SOC., 8, 4453 (1956). ( b ) V. S. Abramov and S. Pall,Tr u d y Kazaii, Khim. Yeknol. Inst. z m S. M . Kirova, 23, 105(1957); Chem. Ahstr , 52, 9949d (1958).

(3) a ) A. N. Podovik and N . P. Denisova, SbornikStalei Obshchei Kham. A k a d . Nauk S.S.S.R., Z 388 (1953);Chem. Absli., 49 8386 (1955). (b) B. A. Arbuzov and B. P.hgovk in , Zhur. Obshchei Khim., 21, 99 (1951); C‘hem.Ahst?., 45, 7002 (1951). c ) V. S. Abramov and N. A. Iliniz,Zhur. Obshchei Khim., 26, 2014 (1956); (‘hpm. Abstr., 51,1822 (1957). (d) G. K:tmai snd V. A. Kukhtin, 7’ridTj Kazan.

Khzm. Tekhnol. Znst. am. S. M . Kirova, N o . 21, 147 (1956);(‘herti. A h s l r. , 5 1 , 11983 (1957). (e) V. S. Abramov andN A. Ilvina, .I. Gen. C‘hem., U.S.S.R., 26, 2245 (1956).

X e + (R0)aPH + RO)~--I’-H + R X (3)

Before discussing the second mechanism, abrief b ut pe rtine nt review of the mechanism of theMichaelis-Arbuzov reaction must he given. Thereaction was discovered first by Michaelis andKa hne 4 and was explored rather thoroughly later

by A rbuzov.6 Th ese autho rs proposed a m echanism(4) which involves an addition reaction to formaquasiphosphonium intermediate which subse-quently decomposes into the products. Myers,Preis, and Jensene present the low reactivity ofcyclohexyl tosylate with tr ieth yl phosphiteas beingin accord with the low reactivity of cyclohexylhalides in SN2 reactions and thus substantiatingth e initial sta ge of th e Michaelis-Arbuzov reactionas an SK2 displacement. Although Michaelis and

RO-E‘< + R’X Rr-P-OR)(Xe) --fe40

R’--P( + R X ( 4 )

Ka hne 4 isolated an interm ediate from triphenylphosphite and methyl iodide which had saltlikep ro pe rtie s, A br am o v a nd P e k h m z ~ n ~ ~nd A bramovand Karp7b,cobtained sirups from trialkyl phos-phites a nd a-,p-dihaloalkyl ethers. Sm ith andBurger7d conclude th at no quasiphosphoniumcompound is involved when bulky secondary alkylhalides are used. Arbuzov an d SazonovaBa hav erecently isolated several more of thes e interme d-iates using triaryl phosphites and alkyl iodides.These compounds are crystalline s; ts. Similarly,

Razumov and Bankovskayasb report the isolationof saltlike intermed iates from th e reaction betweenalkyl phosphinites, Rz-P-OR’, and alkyl halides,Dimroth and Nurrenbacksc report the isolation ofseveral quasiphosphonium salts from the reactionof carbonium ions an d trialkyl p hosphites. Physic0chemical evidence for the existence of these inte r-mediates is presented by Arbuzov and Fuz-henkova. a 3 b

T he over-all mechanism of the M ichaelis-hrbuxovreaction has been dcscribed by Jacobsen, Harvey,

(4) A. Michaelis and R. Kahnr, Bw. 1, 1048 (1898).(5) A. 13. Arbuzov, J . 12uss. Phys, Chem. SOC., 38, 687

(6) T C. Myers, S. Preis, and E. V. Jcnscn, J . Am.Chem. Snc., 76 172 (1954).

(7) V. S. Abramov and A. P. Pckhman, J . Gen. chcm.,U.S.S.R.,26, 81, 171 (1956). (b) V. S. Abrarnov and G. A.Karp, Doklady Akad. Nauk S.S.S.R., 91, 1095 (1953);Chem. Abstr., 4 8 , 9 9 0 6 ~ 1954). (c) V. S. Abramov and G. A.Karp, J . Gen. Chem., 24, 1823 (1954). d) B. 13. Smith and A.Burger, J . Am. Chem. SOC., 5, 5891 (1955).

(8) a ) A . E. Arbueov and N . N . Sazonova, DokladyAkad. Nauk S.S.S.R., 115, 1119 (1957); Chem. Ahslr., 52,6239f (1958). (b) A. I. Razumov and N . N. Biznkovskaya,Dolclarly A k a d . Nauk S.S.S.R., 116, 2411 (1957); (‘hem.Abstr. , 52, 61641 (1958). (c) K. IXmroth and A. Nurrenback,An ieu). Chem., 70 26 (1958).

9) (a) B. A. Arbuzov and A. V. Fuzhetikovtt, DoklarhlAkad. Naulc. S.S.S.R., 113, 1269 (1957). t)) B. A. Arbuzovand A. V. Fuzhenkova, Doklady Akad. Nauk S.S S.R., 114,89 (195i).

(1906).


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534 GARNER, CHAPIN, A N D SCAXLON VOL. 24

and Jensenloa and by Kharasch and Bengelsdorfo band pictured by Saunders as a displacement ofhalogen by phosphite to forma quasiphosphoriiumcompound which, on attack by halide ion, elimi-nates RX to form the phosphonate ( 5 ) . Tha t t he

0 R)2\

(R'-P-OR) + X e + RO)?-I'-R' + RX ( 5 )cI

final stage of t he reaction involves nucleophilicatta ck b y halide ion on the alkyl carbon of the esterhas been demonstrated experimentally. First,Landauer a nd Rydon12 isolated the intermediatefrom methyl iodide and triphenyl phosphite andtreated tdhis mate rial with optically active 2-octanol. The 2-iodooctane which was obtainedas a product was inverted showing clearly thatabimolecular nucleophilic substitution had takenplace, presumably preceded by a rapid ester inter-change between th e octanol and the phosphoniumsalt. Attacking the problem in th e reverse manner,Gerrard and JeacockeI3 reacted trioctyl phosphitecontaining 2-octyl residues from optically active2-octanol with bromine and likewise obtained theinverted 2 -bromooctane. On the basis of the abo veexperimental evidence, the mechanism of th eMichaelis-Arbuzov reaction can be picturcd asfollows:

@( R O h P : + R'X + (RO)J'-R']X* a)

e 0D e /

IXe---R-O- 1'--11' X + R'-l'-(OR)z (b)

(OR),

In the case undcr discussion where the alkylhalide has an activating group on the @-carbonatom, the quasiphosphonium intermediatecan bepictured as going through a less favorable break-down involvinga cyclic transition s ta te which leadsto an intramolecular &elimination similar to that

RX + (ROjZLP + CH,=CII-R"(10) (a) H. I. Jarohsen, R. G. Harvey, and E. V. Jensen,

J . A n t . Chem. SOC., 7, 6064 (1965). (b) Pvi S. Kharaschand I. S. Bengelsdorf, J . Org. ChenL., 20 1356 (1955).

(11) 73 C. Saunders, Some Aspectsof the Chemistryof and7'oxic Act ion of Organic Compounds Containing Phosphorusand Fluorine, Cambridge Univwsity Press, Camhridgc,,1957, p. 95.

(12) S. R. Landnuer and H. N. Rydon, Chem. R. I n d

(13) W Gerrard aud G. J. Jeacocke, J . Chem. SOC.,(Lon&%), 313 (1951).

3647 (1954).

proposed for ester pyrolysis and Chugaev elimi-nations.I4

Th e formation of styrene during the thermal de-composition of qua rterna ry phosphonium hy-droxides and cthoxides which contained p-phen-

ethyl groups has been ihowri by Fentlon and In-gold'5 aiid Hey and Ingold.I6Furth er, the hydrogenbonding ability of the phosphoryl grou p has beenshown clearly by Kosolapoff and McCullough'7and Arbueov and Ra zum ow . Baumgarten andS e t t e r q u i ~ t ' ~ave demonstrated recently th at alkylphosphates, like carboxylic acid esters, undergopyrolysis to give an olefin and the ac id.

T o test the formation of olefin by means of anintramolecular p-elimination through the quasi-phosphonium salt, triphenoxy-@-phenethylphos-phonium iodide, (C6H60)3P~-CH2-CH2-C6H6XI),

was prepared and heated to decomposition at

210-222' and 0.15 mm. Vspor phase chromato-graphic analysis of th e volatile products showedthe presence of styrene and iodobenzene. Thesolid residue was identified as diphenyl p-phen-

ethylphosphonate, (C6H60)-I'-CH2--CH2-CoH~(XII), he major product and the usual Michaelis-Arbuzov product. To show that the styrene wasnot produced as a consequence of th e pyrolysis ofthe ester (XIJ) the diphenyl p-phenethylphospho-nate was heated at 240' and 0.15 mm. for 2 hr.without decomposition. The phosphonate finallydecomposed at 390 . In suppor t of the experi-mental evidence for the olefin formation from thequasiphosphonium salts, the models of thesecompounds show that the hydrogen atoms whichare alpha to the activating group help to form aperfec t five-membered ring wi th one of t he oxygenstha t is at tached to the phosphorus atom. In fact ,these two atom s virtually touch each other.

With the positive charge on the phosphorus,the activated @-hydrogensand the close proximityof the hydrogen and oxygen in a fivc-memberedring, one might expect olefin formation to b e morepredominant. Since there are three alkoxyl groupsattac hed t o the phosphorus, the chances of the in-coming negative ion attacking the same alkoxylgroup which forms the ring is m:de even less favor-able by the fact th:it the other alkyoxylor aryloxylgroups are thrown outward into space where theyare m ore susceptible to a ttack.

(14) For a complete discussion of Intramolecular Elimina-tions see M. S. Kewman, Steric E e*tsin Organic Cheni;stry,h'ew York, John Wilcy Cy Sons, Inc., 195G, pp. 305-14.

(15) G. W cnton nnd C. K. Snaold, J . Chem. Soc.,

10

0

2342 Y929).(16) L. Hey itrid C. K. Ineold. J. Chem. 531 (1933).(17) C. M. Kosolapoff and J . M . McCdloiigh, J . Am.

Cheni. Soc., 73, 53 12 (1051).(18) A. E. Arbuzov iind K . A . llazumova, DolcladyAkad.

A'auL S.S.S.R., 97,443 (1954); Chem. Abstr., 49,9538 (1955).(19) H. E. Baumgarten and R. A. Setterquist, J . Am.

Chert. SOC., 9, 2605 (1957).


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APRIL 1959 MICHAELIS-ARBUZOV REACTION 535

Although it has no bearing on the mechanismofthe Michaelis-Arbuzov reactionor olefin fo rma tion,it should be mentioned here that a large portion ofthe products of this reaction is a nondistillablesirup. This material is always acidic, is water solu-ble, and, presumably, is easily hydrolyzed. Allevidence to date indicates that these materials arepolypyrophosphonates which contain (P-0-P)linkages formed by olefin and alohol eliminationduring t he long heating periods of t he reaction.

EXPERIMENTAL

The p-bromoethylbenzene and the ethyl p-bromopropion-ate were obtained from Matheson, Coleman, and Bell, thelJ2-dibromoethane from Eastman Kodak Co., and thetriethyl phosphite and diethyl phosphonate from Virginia-Carolina Chemical Corp.

p-lodoethylbenzene.A mixture of 92.5 g. (0.5 m.) of 8-bromoethylbenzene, n'g 1.5543, 74.9 g. (0.5 m.) of sodium

iodide and 50 ml. of acetone was refluxed on a steam ba thovernight. The resultant red liquid was separated by filtra-tion and the solvent was stripped. Distillation of t he heavyoily residue gave 92.0 g. (79.370) of material, b.p . 71"/1.1mm., nz: 1.5945.

Diphenyl p-phenethylphosphonate.A 5.0 g. sample (0.009m.) of triphenoxy-p-phenethylphosphonium iodide was al-lowed to stand overnight in excess 10% aqueous NaOH.A white solid formed. The solid was filtered and recrystal-lized from n-hexane to give 2.5 g. (65.2%) of f ine, whiteneedles, m.p. 75-76'.

A n a l . Calcd. for CzoH19P03: C, 71.0; H, 5.62; P, 9.17.Found: C, 71.13; H, 5.44; P, 9.38.

The infrared spectrum of this material was recorded as amelt, on NaCl plates.

Triphenoxy-p-phenethylphosphoniumiodide. A mixture of73.0 g. (0.3 m.) of freshly prepared p-phenethyl iodide and146.2 g. (0.5 m.) of t riphenylphosphite was heated a t128" for 5 days. The reaction mixture was protected frommoisture by "Drierite" tubes. When the resultan t, dark red-brown mixture was mixed with absolute ether, a dark solidfraction precipitated. The ether was decanted and a freshportion was added and the solid became more firm. Thematerial was mixed with an absolute ether, C.P. acetonesolution, in several portions until the color became canaryyellow. Then the solid was extraoted in a Soxhlet extractorwith a mixture of 10 ml. of C.P. acetone and 250 ml. ofabsolute ether until the solid was almost cream color, andth e solvent no longer became yellow. Removal of the solventand drying under vacuum left 28.3 g. of mater ial whichmelted in a sealed tube a t 154-157'. The solid with silvernitrate gave an immediate precipitate which was insoluble

in dilute nitric acid.A n a l . Calcd. for Cz6H2aP031: C, 57.57; H, 4.43; P, 5.72;I, 23.42. Found: C, 56.86; H, 4.63; P, 5.60; I, 23.46

Reaction of triethyl phosphite with I, -dibromoethane.Sevenhundred fifty-two g., (4.0 m.) of l,2-dibromoethane washeated t o reflux at 131". Then 183.0 g. (1.1 m.) of freshlydistilled triethyl phosphite was added dropwise under nitro-gen pressure over a period of 1.5 hr. During the addition ofthe phosphite an d subsequent hea ting of t he mixture t o afinal temperature of 145" over a period of 3 .5 hr., 110.8 g.(1.08 m.) of ethy l bromide was distilled from the reactionmixture through an 8-in. Vigreux and was collected in anattached cold trap. The reaction mixture WBS fractionatedthrough a 15-in. Vigreux column af ter removal of 509.6 g.of unreacted dibromide at atmospheric pressure.

The first low boiling fractions of 33.7 g. consisted of a

mixtu re of diethyl vinylphosphonate, diethy l phosphonate,and diethy l ethylphosphonate as shown by infrared analysisand vapor phase chromatography. Subsequently, 127.0 g.

of die thyl p-bromoethylphos ate , b.p . 90°/1 mm., nzz1.4564 was obtained. Seven seven-tenths grams of anintermediate fraction, n%5 1.4473, which contained sometetraethyl ethylenediphosphonate was followed by thesudden evolution of 13.4 g. of materia l which dropped thehead temperature to 30°/2 mm. and had n; 1.4250 whichalong with its infrared spectrum showed it to be pure di-ethyl vinylphosphonate.

Reactzon of triethyl phosphite with diethyl p-bromoethyl-pbosphonate. Diethyl p-bromoethylphosphonate, 50.7 g.(0.17 m. ), was heated t o 157' and 35.3 g. (0.21 m.) of dis-tilled triethyl phosphite was added dropwise over a 3-hr.period. Dur ing the heating over a to tal of 6 hr., 17.9 g.(0.16 m.) of e thy l bromide distilled. The final reaction tem-perature was 198". Vacuum dist illation of th e pale yellow,nonviscous mixture yielded 28.8 g. of a low boiling mixtureof approximate ly 64.5% diethyl phosphonate , 25.8% diethylvinylphosphonate, 6.9% diethyl ethylphosphonate, and2.9% of a n unknown as determined by infrared and vaporphase chromatographic analyses. A higher boiling fractionconsisted of 16.2 g. of te traet hyl ethylenediphosphonate,b.p. 151-157"/1 mm., n', 1.4397.

Reaction of ethyl p-bromopropionate with triethyl phosphite.Kine ty g. (0.54 m.) of distilled tr iethyl phosphite was addeddropwise over a period of 3 hr. t o 100.0 g. (0.55 m.) ethylp-bromopropionate a t 155". The initial addition of thephosphite caused the temperature to drop to 137" whichtemperature held throughout the reaction. The reactionmixture was heated for 5 hr. after the complete addition ofthe phosphite and 48.4 g. (0.44 m.) of ethy l bromide wasdistilled during t he heating.

'Vacuum distillation of the mixture yielded 21.9 g. ofmaterial , b.p. 66-86"/4-7 mm., which infrared showed tobe die thyl phosphonate and probably dietrhyl ethylphos-phonate , 80.0 g. of et hyl 3-diethylphosphonopropionate,b.p. 114-115"/2 mm., n', 1.4301 an d 24.1 g. of polyethyl-acrylate, n', 1.4662. The distillation cold trap yielded 6.84g. of ethyl acrylate, y 1.3975. The acrylate monomer andpolymer were identified by their infrared spectra.

Reaction of triethyl phosphite with p-bromoethylbenzene.One hundred g. (0.54 m.) of p-bromoethylbenzene washeated to 165", then 90.9 g. (0.54 m.) of distilled triethylphosphite was added dropwise. The temperat ure rose slightlyand maintained itself a t 166-155' when the heat waslow he heat was maintained for approximately 20hr . this period, 33.6 g. (0.31 m.) of ethyl bromidedistilled from the mixture. T he reaction mixture was vacuumdistilled th rough an 8-in. Vigreux.

The first fraction of 43.9 g. was shown by infrared t o con-tain diethyl phosphonate, diethyl ethylphosphonate, andunreacted p-bromoethylbenzene. The second fraction wasmostly diethyl ethylphosphonate, 3.9 g., and t he thi rdfrac tion consisted of 68.8 g. of di ethyl p-phenethylphosphon-ate, b.p. 144-147"/2.3 mm., n2,5 1.4925. The residue in thepot was dissolved in benzene and 3.2 g. of polystyrene w:spTecipitated in methanol. The cold trap contained 10.4 g.of material which decolorized bromine in carbon te tra -chloride and was shown by its infrared spectrum to be mostlystyrene.

Test for the rmal stability of tetraethyl ethylenediphosphonate.A sample of tetr aethyl ethylenediphosphonate was heateda t 211" for 5.5 hr. The ma teria l was pumped down andheated. N o low boiling materials were distilled at 7 0 / 2mm.

Pyrolysis of diphenyl p-phenethylphosphonate.An 8.1 g.sample of diphenyl p-phenethylphosphonate was heated for2 hr. at 240'/0.15 mm. with no decomposition. This mat er iJwas heated again for 4.5 hr. a t 250-305"/5 mm. still with-out decomposition. The material was recovered, recrystal-lized, and the melting point checked. Then the sample washeated a t atmospheric pressure up to 390" to give a trace

of water and a viscous, brown residue which was stronglyacidic. The odor of s.tyrene was strong in t he att ached dryice trap, but no styrene was isolated. The infrared spectrum


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536 McBAY TUCKER, A N D GROVES VOL. 24

of the viscous, brown residue showed polystyrene to be The dark solid residuc in the pyrolysis tube was re-absent. crystallized from n-hexane as long white needles, m.p. 75.1-

Pyrolysis of triphenory 8 pheltethylphosphonillm iodide. A 75.6’. A mixed mcltirig point with authenticated diphenyl10.0 g. sample of triphenoxy-B-phenethylphosphonium 8-phenctliylphosphoriatc of m.p. 75.0-75.3’ was 75.0-iodide was dried overnight under vacuum and then was 75.6‘.heated a t 210-220’/0.15 mm. over a period of 4 hr. The dryice traps which were attached to the pyrolysis apparatus

contained a Rmnll amou nt of liquid which smelled of iodo-benzene. The infrared spectrum of this material confirmedthe presence of iodobenzerie and hinted a t th e prescnce ofstyrene. Vapor phase chromatographic analysis of thismaterial showed the presence of a emall amount of styrene.

Ackn,ywledgm&: “‘he au tho rs ar e ind ebte d toPeter Shapras for the infrared and vapor phasechrom atograp hic ana’yses*

SPRINGFIELD , MASS.

[CONTRIBUTION FROM THE CHEMICAL LABORATORIES F ~ ~ l o R E I i O l J S E OLLEGE A N D THE ATLANTA UNIVERSITY]

Reactions of Methyl and Ethoxy Free Radicals in Chlorohydrocarbons AComparative Study of the Use of Diacetyl Peroxide and Diethylperoxydicar-bonate as Agents for Linking Alpha Carbon t o Alpha Carbon in Some Chloro-

Subs ti tu ted Aralkyls ’HEXRY C. McBAY, OZIN TUCKER, A N D I’AUIA T. GROVES

Received September2.4, 1058

Iliacetyl peroxide reacts with approximatel$ cqiial facilitv with the chloro-substituted aralkyls, 3,Pdichlorotolricne, 2,6-dichlorotoluene, and a,a-dichlorotoluene (benzal chloride) to give the corresponding chloro-substi tuted bibenzyls derivedfrom the dimerizations a t the alpha positions. I>iethvl peroxydicarbonate reacts with 3,4di chlorot oluene n the same manneras does diacetyl peroxide, producing 1,2-bis(3,4dichlorophcnyl)ethane (3,4,3’,4‘-tetrachlorobibenzyl) and with essentiallyequal yield. Diethyl peroxydicarbonatc gives a poorer yield of the same dimer, 2,6,2’,6’-tctrachlorobibenzyl, s obtainedfrom the reaction of diacetyl peroxide with 2,6-dichlorotoluene. Practically none of the dimer, tetrachlorotolane, obtainedfrom the reaction of b e n d chloride with diacetyl peroxide, is produced when diethyl peroxydicarbonate is used s the link-ing agent. Dia retyl peroxide links p-isopropylbenzal chloride ur symmetrically with itself to produce 1 I-dichloro-1-p-isoprop~vlphen~l-2-methy1-2-(~,w-dichloro-p-tolyl)propanexclusively, while diethylperoxydicarbonate links n-isopropyl-

benzal chloride symmetricitlly with itself to produce exclusively 2,3-di-(wJw-dichloro-p-tolyl)-2,~-dimeth~lbutane.

Of t he sev eral possible mod es of re action av ail-able to free radicals generated in solution, the onctaken by a given free radical depends only in pa rtupon t he natu re of th e free radical itself. Ex terna lfactors of im portance are temperature and th enatu re of th e coreac tant. It must be kept in mindthat there is competition between solvent andparent substance, despite its low concentration indilute solutioii, as coreactants for the free radical.Several factors determining the relative effective-ness of the solvent molecule in such competition

have been disclosed. Th e relative streng ths of thebonds holding the univalent atoms in the solventmolecule, which strength largely determines theease with which the bonds holding these univalentatoms succumb to cleavage by free radicals, hasbeen termed the energ y factor.2 Th e na ture and thepositions of th e subs tituen ts in th e solvent moleculehave a pronounced effect upon the ease withwhich said m olecule yields an univalent ato m to thecleaving action of ethoxy free radicals,but thesefactors seem to have little or no effect upon the

(1 ) Presented in par t before the Organic Division of theAmerican Chemical Society a t th e 128th National Meeting,Kcw York, Septemtxr 1954.

(2) X C. McBay and 0 . Tucker, J . Ory. Cheni., 19, 869(1954).

analogous action of such molecule toward methylfree radicals. A previous paper3 reports th 2t hy-drogen atoms are readily cleft from solvent mole-cules by methyl and by ethoxy free radicals whenthese hydrogens are attached to the same carbonatom w ith methyl and/or phenyl groups. The sub-stitution of carbomethoxy groups for the methyland/or phenyl groups produces no noticeable ef-fect upon the tendency of the solvent to dona te ahydrogen atom to methyl free radical but greatlyreduces its tendency to yield hydrogen to t heethoxy

free radical. Thi s unusua l effect of th e carbo-methoxy group upo n th e course of these free radicalreactions has been termed the repulsion factor.Th is paper reports a continu ation of the se studies.It attempts to show that the introduction ofchlorine atom s into positions adjacent to th e“preferred” seat of attack for the cleavage re-actio ns of these free radicals ha s little or no effecton the percentage of cleavage exhibited by t hemethyl free radical and no effect whatever on t hesite of its cleavage attack. On th e other hand ,th e imme diate proximity of th ese chlorine atom s tothe prcferred seat of a tta ckdecreases the percentage

( 3 ) 13. C. McBny, 0 . Tuckor, and A. Milligan, J . Ory.Chem., 19 1003 (1954).

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