Metal cluster catalysis. 2. Selective reduction of nitrobenzene catalyzed by rhodium carbonyl cluster anions. Evidence for water gas shift reaction

319

Journal of Molecular Catalysis, 5 (1979) 319 - 330 @I Elsevier Sequoia S.A.. Lausanne - Printed in the Netherlands

METti CLUSTER CATALYSIS. 2. SELECTIVE REDUCTION OF NITROBENZENE CATALYZED RHODIUM CARBONYL CLUSTER ANIONS. EVIDENCE FOR WATER GAS SHIFT REACTION

ROBERT CHARLES Departrqent (U2i.A.) (Received

C_ RYAN, GARY M. WILEMON. U. PITTMAN, Jr. of Chemistry. January

18,197s)

The Uniuersity

MARK

P_ DALSANTO

of Alabama,

University,

BY

and Alabama

35486

2

Summary The rhodium cluster compiex, Rhs(CO),s, has been found to catalyze the homogeneous reduction of nitrobenzene to aniline at temperatures above 80 “C in the presence of N,N-dimethylbenzylamine, using any one of the following reducing gases: (1) H,/CO,(2) Ha, (3 j CO/HsO. The reductions are highly selective and aniline was the only product detected_ The same result was obtained using Amberlyst A-21 resin beads which contained polymerbound NJV-dimethylbenzylamine moieties which, in turn, immobilize the rhodium clusters_ It was shown, by using DaO, and following deuterium incorporation into the resulting anihne, that the water is the source of hydrogen when CO/Hz0 was used. When nitrobenzene is absent, this catalyst system promotes the water-gas shift reaction_ Unlike aromatic nitro groups, aiiphat$c nitro groups were not reduced. However, the water-gas shift reaction was cataiyzed, The kinetics of aniline formation were first order in nitrobenzene and the effect of pressure on the reaction is described. Use of the resin catalyst led to lower rates and a remarkably air sensitive catalyst systemrelative to the homogeneous reactions.

Introduction Three areas of homogeneous catalysis have attracted increased attention recently: (1) the use of metal cl~stms in catalysis [1,2], (2) the “heterogenizing” of a homogeneous catalyst via attachment to an inert support material (e.g.. an organic polymer or glass) [S] , (3) the water-gas shift reaction [4,5]. Because of our interest in these areas [6,71, we sought a cluster

320

system that could be immobihzed on a polymer and which would catalyze the water-gas shift reaction while immobilized_ The advantages of polymeranchored systems, including ease of catalyst recovery and ease of product separation, have been reviewed extensively 13, ‘7]_ However, polymer-attached catalysts for the conversion of carbon monoxide and water to molecular hydrogen have not been examined in depth. One cIuster system which has been attached to a polymer is the rhodium carbony amine complex [8] [NRsH] l [RhJCO),_]-_ The amine, NJV-dimethyIbenzyIamine, is incorporated in a styrene-divinylbenzene polymer. Such polymer-bound rhodium clusters have been thought to be involved in the hydrogenation of activated olefins using carbon monoxide and water at high pressure e 800 p_s_i_) [9] _ Although a water-gas shift reaction was imphed, there was no direct evidence that the hydrogen did, indeed, come from the added water. HydroformyIation and hydrogenation of olefins to alcohols using carbon monoxide and hydrogen has been catalyzed by homogeneous and polymer-bound amine-rhodium clusters IS] _ HomogeneGus reactions which employ rhodium ciuster catalysts include the conversion of syn gas to methanol and ethylene glycol [lo], and the hydrogenation of nitrobenzene to anihne using a high pressure of carbon monoxide and water [ll] _ In order to study the versatihty of these homogeneous and polymerbound cIusters, we examined their use in the reduction of a variety of substrates [12] _ This paper reports the selective catalytic reduction of nitrobenzene to aniline under mild conditions by homogeneous and polymerbound rhodium carbony cIuster anions. A variety of reducing atmospheres was used including hydrogen, water/carbon monoxide, and a lrl hydrogen: carbon monoxide mixture_ Aromatic nitro compounds were chosen because their known reductions by homogeneous catalysts have inherent practical limitations. For exampIe, the reduction using iron carbonyl catalysts [ 13,141 under mild conditions is essentially stoichiometric in iron_ Whether this reduction was conducted in refIuxing benzene/methanol [ 131 or at room temperature in base with [18] -crown-6-ether [14], the ratio of substrate to c&aIyst is approximateiy two in both cases_ Another catalyst which has been reported is the phosphine nicke1 complex, (PPh,),Ni&, but this reduction requires an expensive reducing agent, NaBH, [ 15]_ Second-row transition metal complexes have also been examined for aromatic nitro reductions_ R~s(C0)~z required. high temperatures (140 - 160 “C) and also high pressures (2 800 p_s_i_ of I:1 Hz:CO) 116 J _ At low hydrogen partial pressures, there was significant formation of 2,2’-diphenylurea. Monomeric ruthenium complexes (e-g_, (PPhs),RuCI,) have been reported selectively to reduce aromatic and aliphatic nitro compounds to amines under hydrogen pressure (2 100 p&i_) and temperatures near 120 “C [17,18] _ In addition to providing evidence for a homogeneous water-gas shift reaction, the rhodium cluster anions used in this study are superior to the catalytic systems mentioned above for the reduction of nitrobenzene.

321

Results The hexarhodium carbonyl cluster, Rhs(CO),s, ing to the method of Chaston and Stone 1191. RhCI,-x

H,O

CO (700

p.s.i.)

CH30H,

60 “C

’

was synthesized

(75%)

RhcACOh,

accord-

yield

The amine-rhodium catalyst was then made in situ by mixing Rhs(CO),s, waters and either homogeneous or polymer-bound NJV-dimethylbenzylamine (DMBA) in THF_ Nitrobenzene was then selectively and quantitatively hydrogenated to aniline with this rhodium cluster catalyst system_ These nitrobenzene reductions were accomplished at 80 - 120 OC using a total gas pressure of 100 - 700 p_s_i_g_ The reducing gas could be Hz or Hz:CO(lrl) or CO_ In ail cases, the only product was aniline_ TO2

4

0

0P

-DMBA or DMBA + Rhfj(C0) lUO°C,

TRF

NH2 16

-I- “20

co or q?/coor H-2

4

0

Further hydrogenation of aniline to cyclohexylamine was not observed, even at long reaction times under hydrogen pressure_ At high carbon monoxide and low hydrogen pressures, other byproducts (such as 2,2’-diphenylurea, which was formed in significant quantities when Ru,(CO),~ was used at low hydrogen pressures [16] ) were not produced. Table 1 summarizes the results of sample reductions_ In ah cases the amount of nitrobenzene consumed equals the amount of aniline produced according to electronic integration of g.1.c. data using the internal standard technique_ As seen from reaction 1 (Table I), no hydrogenation of nitrobenzene occurred without DMBA, using Rhs(CO)rs at 100 “C and 800 p.s.i. (Hz:CO l:l)_ However, the addition of DMBA to the reaction in an approximate 33O:l DMBArRh, ratio, results in the-quantitative formation of aniline at 100 “C and 700 p_s.i_ (1:l H2:CO)_ Kinetic data for example reductions.are illustrated in Fig. 1. A good first-order rate dependence is secured for the decrease in the concentration of nitrobenzene as a function of time. The rate constants are evaluated from the slopes of the lines for the first 80% of the reaction, and these are listed in Table 1. Reactions (2 - SP), using 1 :l Hs:CO, exhibit significant changes in rate a& a function of temperature and total gas pressure_ Time for completion of the reaction approximately quadruples as the total pressure is increased from 350 to 700 psi. At 350 p.s_i- there is more than an order of magnitude decrease in reaction time from 45 h (91.0% completion) to 4 h (100%) as the temperature is raised from 80 to 100 “C. When the catalyst system was not equilibrated prior to the start of the reduction (see Experimental Section), there was an induction period ranging from 70 to 480 min before product formation was observed in reactions

223 213 243 23,6 24,9 25,6 16,6 15,9 17,6 310,o 22,5 19,3 19,6 ’ 20,9 23,9 22,5 92,9 92,9

22,5

0,022 0,062 0,062 0,066 0,066 0,071 0,067 0,064 0,063 0,068 0,066 0,066 0,063 0,067 0,069 0,062 0,064 0,070 0,070 H2:C!0 100 Hz:CO 100 Hz:CO 80 Hz:CO 100 H2:C0 100 H2:C0 100 H2:C0 100 H,:CO 100 H2:C0 100 H,:CO 100 HI1:CO100 Hz$0 106 100 H2 100 132 100 H2 100 co 120 co 120 co 120 co

800 700 350 350 350 175 100 350 350 350 350 360 350 350 350 350 350 350 350

15 16 45 4 3,3 203 702 20,8 15,5 36,9 137,5 48 5 4 3,3 100 8 98 72

O(O)

lOO(22.3) 91,0(19,8) lOO(24-E) 100(23,6) 36,7(21.6) 30,0(20.5) B4,5(16.6) 70,9(11.3) 35,3(16.0) 28,3(87.7) 60,0(11,3) lOO(19.3) B2,0(18,1) 32,1(17,2) 33,0(19,8) 90,O20,3) 79.0f 48,O’ 0,360 -

1603

13,2 14,2 3,97 1,37 0,784 0,584 0,0379

2,48 0,388

Temp, Pressure Reactiontime Total conversion,% Ratoconstant to aniline(mmol)’ (x 10” min-I) (“C) (psi6) (h)

aInternaistandard(o-xylene)wasadded to ail renctions( 100mmoi/l,5 mmolnitrobenaene),The solventused wasa THPwatermixture.The amount of wateradded was0.5 ml, EnoughTMPwasadded to the reactionsolution to bringthe total volumeto 50 ml, In each reaction,except number1,20,4 mtnolof N,N~ciimotbylbenxyiamine (DMBA)wascharged either homogeneouslyor attachedto the polymer,Tke polymersalwayscontained1,4 meq of DMBAper ml of olymer beads,bllPr’refersto reactionwith polymerattachedamine,CMiiiimoies of Rhc(CO)lechargedto the reactor,(PNo DMBAwasadded.‘H2:COis a 1:l mixture, rmmolof anilinedeterminedby g,l,c,internalstandardmethod,sSubstrate not injectedto start reaction,hBeadsd&d under vacuum(0.1 mm) for 4 hour8at 25 “C,‘Beadscrushedunder liquid N2 and dfiodundervacuum(O-1mm) for 4 hour8at 25 “C.‘Polymerrecycledfrom llP, “D20 (6,5 ml) wasu&dIn place of water, No internalstandardwasadded to the reaction,The % conversionis basedon electronicintegrationof peak areas,

$ 4g 5 6 7 8P 9Ph 1OP’ 11P. 12P’ 13s 14 15P 16” 17 18” 19P

Id

Reaction Nitrobonzene Catalyst Gas“ no,b (mmol) (mmol)’

TABLE1 Roducticnof nitrobenzenecatalyzedby homogonoousand polymer-anchored NJ&dimothylbonzyiamine and Rhs(CO)la

323

0.

100.

200.

300.

400_

500.

600.

700.

TIME(min)

Fig_ l_ First order rate plots of the reduction of nitrobenzene catalyzed by homogeneous and polymer-anchored NJV-dimethylbenzylamine/Rh~(CO)~~ using 1~1 H,:CO at 100 “C. Reactions 2, 5, 7 and 8P refer to the reaction numbers in Table 1.

2 - 4. In order to examine the cause of this delay, the catalyst system was pre-equihbrated under reaction conditions before the nitrobenzene and the internal standard were added (reaction 5, Table 1). A plot of the kinetic data (Fig_ 1) reveals that now there is no induction period, suggesting that prior formation of a catalytically-active species is necessary_ A small rate increase (from 13.2 X 10-a mine1 to 14.2 X 10-a min-‘) was observed as the pressure was decreased from 350 p.s.i_ (reaction 5) to 1’75 p.s.i. (reaction 6) using the pre-equiiibrated catalyst. Another decrease in pressure to 100 p.s.i_ resulted in a sharp decrease in the rate constant to 3.97 X 10-a min-I. These results for the homogeneously catalyzed hydrogenations, using a lrl Hz :CO gas mixture, indicate that high rates are favored by high temperature, low pressure to a minimum of 175 p.s.i., and prior formation of a catalytically active species. The rate constant (1.37 X 10m3 mine’) for the reaction using DMBA bound to a commercial (Amberlyst A-21) styrene-divinylbenzene macrorecticular resin

G3-Q

cR2N(C~3?2)

was an order of magnitude smaller than that for the homogeneous run (13-2 10m3 min-‘) under the same conditions. Rate decreases associated with the use of swellable, polymer-bound catalysts have been observed previously 120 - 23]_ These have been attributed to slow diffusion of substrates to the active catalytic sites within swollen resins. Diffusion control of the rate may not be as important a factor when macrorecticular beads are used (versus

X

324

microporous resins) because the active sites are concentrated on the outer surfaces of the particles [ 24]_ Therefore, the slow diffusion of substrate into resinmatrixchannels thatcccurswith microporousresins(land 2%crosslinked) may te minimized using macrorecticular resins. In fact, with a significant rate enhancement was polymer-attached DMBA and RhE(C0)16, reported in the hydrogenation of activated olefins [9] _ The cause of the rate decrease in the present study, as against the increase reported in ref. 9, is unknown_ We did note that the resins employed here exhibited a swelling factor of l-5 in THF after they had previously been dried. Consequently, rhodium cluster sites may actually exist fairly deep within the resin matrix. AItematively, it is known that both the dry and the “swohen” structure of macrorecticular_resins is a complex function of the solvent/nonsolvent ratio, temperature, crosslink density, etc., used in their manufacture [24] _ In certain cases, tiny spheres are, in turn, agglomerated into iarger spheres. The fraction of void volume, the channel size, and the channel depth leading to the small spheres within the huger bead, could play a role in diffusion rate retardation [ 243 _ To test particle size effects, the starting DMBA-resin was subjected to grinding under liquid nitrogen_ The surface area was greatly increased using this procedure_ However, no rate enhancement was observed when this pulverized resin was employed (see run IOP, Table 1). Indeed, the observed rate was somewhat slower_ Easy recycling was not possible using the polymer-attached cluster catalysts because the immobilized cataIyst was far more air sensitive_ The polymer catalyst could be successfully recycled only with great care (see Experimental Section)_ For exampIe, the homogeneous rhodium-amine catalyst was still CataIyticalIy active after exposure to air for over 60 min, but the polymer-bound species had less than a 10 s lifetime in air prior to complete decomposition_ The beads which were crushed and dried before use aIso had the same very short lifetime in air_ By first drying the resin beads at 25 “C for 4 h (0.1 mm) (but not crushing them), a rate constant of 0,788 X 10B3 mine1 for the hydrogenation reaction was observed_ It is interesting to note that the lifetime of these dry, uncrushed catalyst beads, after reaction was over, was one hour in air_ Drying removes a significant amount of water which is present in the resin as obtained commerciahy. A change in reducing atmosphere from a 1:l Hs:CO mixture to pure hydrogen resulted in a slight increase in rate for the homogeneous reactions_ For example, the rate constant increased slightly from 13.2 X 10m3 min-r to 16-2 X low3 min-1 (run 5 us_ 14, Table l)_ The reactions using hydrogen atmospheres alX exhibited an induction period_ When the catalyst was equilibrated before introduction of the substrate, the delay in aniline formation was reduced (see Experimental Section)_ Whether this induction period could be eliminated entirely by means of even Ionger equilibration times has not yet been studied_ A dramatic increase in reaction time (to about 100 h at 100 OC) is observed upon changing the reducing atmosphere from 1:l H,:CO to pure CO.

325

However, no loss in selectivity to aniline occurred. The rate increased by more than an order of magnituae in the reductions employing a pure CO atmosphere when the temperature was raised from 100 to 120 “C. The source of the hydrogen in these reductions appears to be the added water, as was implied previousIy in related reductions using cluster cataIysts [9, ll] _ Water was confirmed as the hydrogen source in labeling experiments. When D20 was used, aniline was produced with 90% deuterium incorpomtion at the amino group, as determined by n.m.r. This strongly suggests that the amine-rhodium cIuster is catalyzing a water-gas shift reaction under mild conditions_ The selective reduction of nitrobenzene to aniline using carbon monoxide and water was also accomplished using the polymer-bound DMBA and Rhs(CO)ls catalyst system. The pressure used (350 p.s.i.) was less than haIf that previously used in substrate reductions using carbon monoxide and water [9,11].

c3 0

DMBA +

NO2

CO

+

or

D20

0

P

-DXBA

=6 (CO) 16, ?XXE’ 35opsi 1200,

w o-

0

N-D2

In order to prove that this rhodium cluster caealyst could, indeed, catalyze the watergas shift reaction, sample runs were carried out at 120 OC under 350 p.s.i. of carbon monoxide and 60 p.s.i. of methane (interi% standard) pressure without nitrobenzene present. Hydrogen production was demonstrated by gas chromatographic studies of the gas phase. Next, it was shown that the water-gas shift HZ0 + CO

Rh,(CO),, 120 O. DMBA THF,glO

l

Hz+CO,

p.s.i.

took place in the presence of ahphatic nitro groups. For example, at 120 “C under 340 p.s.i. of carbon monoxide and 55 p.s.i. of methane, hydrogen evolution in the presence of nitropropane occurred at about one third the rate of that generated in the absence of nitropropane. Finally, when nitrobenzene was present, no hydrogen evolution was observed but aniline was obtained. These results strongly suggest (but do not prove) that the water-gas shift is taking place, and this serves as the source of hydrogen for anihne reduction.

also

Discussion

:

Despite the selective nature of the reduction using Hz, Hz/CO, or CO/ under a variety of conditions, the composition of the active cat&ytic species was not elucidated. The infrared spectrum of the homogeneous solutions (after reaction) indicated that at least two rhodium cluster species were present. Strong bands at 2 050,2 000,182O and 1770 cm-l are believed to Hz0

326

be due to [Rh12(CO)s0]2while a very strong band at 1960 cm-’ suggests the presence of the [Rh7(CO),,] 3- anion [ 25]_ These same species were previously seen when DMBA and rhodium carbonyl clusters were used to hydroformy1at.e olefins [ 81 and hydrogenate activated olefins [ 9]_ Thus, cluster anions probabIy pIay a major role in the formation of the catalytically active species_ The extreme air sensitivity of the resin-attached catalysts precluded an infrared study of these systems. However, an instantaneous color change of the resin, from red to green, occurred upon opening the reaction vessel to air. The same color change was reported by Kitamura et aZ_ 191, who attributed the green color to the [Rhs(CO)1s]2dianion- They claimed this dianion was the active hydrogenation catalyst_ This cluster, however, was not directIy observed by Wbitehurst ef aZ_ [8] during oIefin hydroformyIations with resin-bound rhodium-amine clusters_ The infrared spectra in that study were taken under the actual conditions of the reaction. We suggest the first step probably involves reduction of the rhodium cluster to an anion. The anion, as suggested by the Mobil group 183 , is probably bound to the resin, which explains the excellent retention of rhodium even in flow systems. 2+H~0+Rh(j(CO~1&--+

2H

[Rhx(CO) y] -

Under reaction conditions, more than one cluster may be generated. It seems likely that the homogeneous system is rather air stable after a reaction has been compIeted, because no oxygen-sensitive intermediates remain after the reaction is terminated. Oxygen-sensitive intermediates may be isolated within the resin matrix, contributing to the great air sensitivity of the resinanchored cataIysts_ Despite the uncertainty over the identity of the actual catalytic species, this cataZyst is selective for the reduction of nitrobenzene to aniline. The rates, under miId conditions and a 35011 substrate: catalyst ratio, are superior to previously cited homogeneous cataIya&s used to reduce nitrobenzene. The catalyst stability during the reaction was impressive. Molar turnovers of 1 350 moles of aniline per Rh, cluster were obtained in single batch reactions- Furthermore, the catalyst from these reactions could be recycled again. An extension of this work to ahphatic nitro compounds was made_ However, I-nitropropane was inert when subjected to the DMBAH2/C0 catalyst system_ Thus, a mixture of Rh,(CO),DMBA--Elh6 WItTO2

H2/CO.

(CO)

H2O

200--5OOpsi 80° -1200

16

, no

reduction

327

aliphatic and aromatic nitro groups can be selectively reduced to give arematic amines and aliphatic nitro compounds_ The application of this catalyst to selective reductions such as that shown below, is being pursued [12]_

Experimental THF was refluxed over CaHz for at least 24 h and then distilled under nitrogen immediately prior to use_ Nitrobenzene, nitropropane, and o-xylene were dried over CaCl, and distilled- The water was distilled once. The D,O (99.84 mole %) (Bio-Rad Laboratories) and NJV-dimethylbenzylamine (Aldrich Chemical Co.) were used as received_ All solvents were flushed with nitrogen before placing them in the reaction vessel_ Nitrogen, hydrogen, and carbon monoxide (39 + %) were obtained commercially and used as received_ Rhodium trichloride hydrate (RhCl, -XI&O) was purchased from Strem Chemical Company and used in the preparation of Rhs(CO)16_ Resin beads (Amberlyst A-21), cross-linked with 8% divinylbenzene, and containing 1.4 meq/ml of bound NJV-dimethylbenzylamine, were purchased from Mallinckrodt. The beads, as received or after crushing, did not swell in THF. The beads that were first vacuum dried had a swelling ratio of 1.5 (sw&ed volume/dry volume)_ Analytical g.1.c. separations were done on a Hewlett-Packard Model 5701A gas chromatograph equipped with a Hewlett-Packard Model 3380A recorder integrator_ A 10 ft X l/8 in_ column of 12% OV-101 deposited on Chromosorb W (acid washed - DMCS treated) was programmed from a starting temperature of 100 OC, held for 4 min. and then increased at the rate of 16 “C min to a final temperature of 190 “C to effect efficient product separation_ Gas analyses employed a 5A molecular sieve column and nitrogen as the carrier gas. Methane was used as an internal gas standard to alIow quantitative studies of hydrogen generation_ The preparative scaIe g.1.c. separations were performed on a Hewlett-Packard Prepmaster Model 776 chromatograph using an 8 ft X 1 in_ 20% UC-W98 column at 150 “C. The i-r_ and n_m_r_ were obtained on Beckman-IR-33 and Perkin-Elmer R20B instruments, respectivelyThe stainless steel autoclaves, 150 ml capacity, used in these reactions were washed thoroughly and dried at 120 “C for at least 6 h prior to each run_ : Reduction of nitrobenzene In a typical reaction, the autoclave was cooled under a stream of nitrowater, THF, and either NJV_dimethyIgen and charged with Rh&CO&,

328

benzylamine or Amberlyst A21 beads in amounts listed in Table 1. The vessel was flus-hed three times with the gas to be used in the reaction and then pressurized_ The vessel was then placed in an oil bath preheated to 100 “C where it was shaken for at least 6 h prior to the start of the reaction_ The reaction was begun by iujecting a mixture of nitrobenzene and o-xylene (internal standard), under pressure, into the vessel. A constant-pressure regulator system, described elsewhere [ 201, maintained the desired pressure (Table 1) in the autoclave_ Some reactions (Table 1) did not have the substrate injected to start the reaction_ These runs contained all components, including substrate, before the autoclave was placed in the pre-equilibrated oil bath. Recycling

of polymeric

catalyst

Many attempts at recycling the polymeric catalysts resulted in decomposition to brown polymers which were not catalytically active and could not be regenerated even at high temperature and pressure_ Successful recyclir_g could be accomplished only by rigorous exclusion of oxygen, because even a brief exposure to the air of ten seconds resulted in complete deactivation ofthepolymericcataIyst_Fastfiltrationofthepolymerinaglovebag in the dark. and immediate recycling of She catalyst under hydrogen and carbon monoxide pressure, resulted in a polymer which was still catalytically active. Kinetic data The kinetic results were obtained by sampling the reaction at various times and using a g.1.c. internal standard technique to obtain the concentration of product and the remaining nitrobenzene. By plotting the logarithm of the initial substrate concentration (Ca) divided by the remaining nitrobenzene concentration (C,) us_ time, straight line plots were obtained_ The first order rate constants were obtained by least-squares fitting_ The correlation factor for each of the lines was greater than O-99 except for reaction 2 where it was O-966_ Labelling experiment The product from the reaction using carbon monoxide and Da0 was collected via preparative g.1.c The “deuterated” aniline obtained was identified by comparing the i.r_ and n.m.r_ spectra with an authentic nondeuterated sample. The number of amine hydrogens was determined by integration of the n-m-r_ spectra where the phenyl moiety was used as an internal standard. Aniline; i_r_: 0x-n 3 400 cm 1, , Vx_n 2 500 cm -I, Vc__N 1310 cm-‘, vC__N 1190 cm-r; n-m-r_: 6 3.4 (s, 0.2H, N-H), 7.4 - 6.2 b (m, 5H, phenyl) Other

nitro

compound

reductions

Attempts were made to reduce I-nitropropane with the homogeneous catalyst at 100 “C and 350 p.s.i_ (HzrCO l-l)_ No reaction was observed after 70 h.

329

Studies

of hydrogen

evolution

To a 150 ml autoclave, Rhs(CO)Is (0.070 2 g, 0.066 mmol), Hz0 (2 ml, 110 mmol), DMBA (2.76 g, 20-4 mmol), nitrohenzene (12.04 g, 97.8 mmol) and THF (45 ml) were charged_ The reactor was pressurized to 350 pk. with carbon monoxide and then to 410 psi. (total) with methane (25-4 mmol)_ It was then placed in a 120 “C external oil bath. Gas samples were withdrawn periodically for hydrogen analysis_ No hydrogen was observed but aniline formation occurred. Identical reactions were run except that I-nitropropane (2 ml) was added in place of nitrobenzene. In these, hydrogen evolution occurred_ For example, 1.9 mmol of hydrogen were detected in the gas phase after 64 h. Since sampling techniques caused variations in pressure, accurate kinetics were not obtained_ Identical reactions were run except that no nitro compound was. present. Under these conditions hydrogen generation was detected. After 64 h, 4-S mmol of hydrogen were observed in the gas phase_

Acknowledgements The authors gratefully acknowledge partial support of this researzh by the National Science Foundation, Grant Number DMR77-06810_

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19 20 21 22 23 24 25

S_ H. H. Chaston and F. G. A. Stqne, Chem. Commun., (1967) 964. R. M_ Hanes, Ph_D. Thesis, Univ_ Alabama, 1976_ C. U_ Pittman, Jr., R. M. Hanes and L. R. Smith, J. Am. Chem. Sot., 97 (1975) 1 742. R_ H. Grubbs, L_ C_ Kroll and E_ M. Sweet, J_ Macromok Sci., Chem., A7 (1973) I 047_ W_ Heitz, J. Chromatography, 53 (1970) 37_ W_ Heitz. Adv_ PoIym_ Sci_. 23 (1977) I_ S_ Martinengo and P_ Chini, Gazz. Chim_ Ital_, 102 (1972) 344_