Notizen 1823
Reduction of Carbonyl Compounds by Catalytic Hydrogen Transfer from 1,4-Butanediol
Radovan M arčec
‘"Rudjer B o sk o v ic” Institute, Zagreb, Croatia, Y u goslavia
Z. Naturforsch. 39b, 1 8 2 3 -1 8 2 4 (1984);
received April 3, 1984
H ydrogen Transfer, Carbonyl C om pounds, 1,4-B utanediol R uthenium (II) C om plexes
H ydrogen transfer from appropriate hydrogen donors to unsaturated substrates catalysed by transi
tion m etal com p lexes offers som e advantages over hydrogenation with m olecular hydrogen [1], T hese reactions have been carried out mainly with stoichiom etric or excess am ounts o f primary or se c ondary alcohols [2—7], hydroarom atic com pounds [8] and formic acid [9] as hydrogen donors.
A lthough bis primary diols exhibit relatively high propensity for hydrogen donation [10, 11], little at
tention has been paid to the em ploym en t o f these com pounds as the source o f hydrogen in hydrogena
tion reactions. The aim o f the present investigation was to exam ine the potential use o f 1,4-butanediol as the source o f hydrogen in the catalytic reduction o f carbonyl com poun ds, using ruthenium (II) com plexes as hom ogen eou s catalysts.
Experimental
Carbonyl com pounds and 1,4-butanediol were commercial products, and were distilled before use.
R uthenium (II) complexes, R uH C lC O (P P h3)3 [12], RuCl2(PPh3)3 [13] and R u H2(PPh3)4 [14] were p re
pared by published m ethods.
In a typical hydrogen transfer experim ent, car
bonyl com pound (10 m m ol), 1,4-butanediol (5 mmol) and ruthenium (II) complex (0.03 mmol) were placed in a glass am poule, and the air was re placed with nitrogen. The scaled am poule was placed in a therm ostated oil bath and heated at 140 °C for 20 h. Reaction products were analysed by GLC. The analysis was carried out with a H P 5790 apparatus connected to a H P 3390 A calculating in
tegrator. Separation of reaction products was accom plished using Carbowax 20 M on a C hrom osorb W HP 80/110 mesh column.
Results and Discussion
In the reaction betw een equim olar quantities of carbonyl com pounds and 1,4-butanediol in the p re
sence of catalytic am ounts of ruthenium (II) corn-
0 340-5 0 8 7 /8 4 /1 2 0 0 -1 8 2 3 /$ 01.00/0
plexes, carbonyl compounds were reduced to corre
sponding alcohols, while 1,4-butanediol was con
verted to y-butyrolactone:
2 R C O R ' + H O (C H 2)4O H R u (n ) complex— ^ 2 R C H O H R ' + / c=0
cr
The reactions were carried out in bulk without sol
vent, and some representative results are presented in Table I. Am ong ketones an excellent yield was observed for the reduction of cyclohexanone to cyclohexanol. By increasing the ring size of the cyclic ketone, the yield on the cyclic alcohol dropped con
siderably. This is probably caused by steric hindrance of the more bulky groups. Aryl alkyl ketones were reduced to secondary alcohols in good yields. In con
trast, 4-m ethyl-2-pentanone is relatively resistant to reduction. When ketones were reduced with secon
dary alcohols as hydrogen donors, the maximum yield of the reduced product was determ ined by the equilibrium existing in such systems [2]. This is not the case in the system presented here, where the yield of the reduced product was determ ined kineti- cally.
In the reduction of a,/?-unsaturated ketones, the C = C bond undergoes reduction before the carbonyl group. However, addition of the second equivalent of 1,4-butanediol caused reduction of a saturated
Table I. Reduction o f carbonyl com pounds by hydrogen transfer from 1,4-butanediol catalysed by
R uH C lC O (P P h3)3.
Carbonyl com pound Product Y ield [%]a
C yclohexanone Cyclohexanol 95
C ycloheptanone Cycloheptanol 58
C yclooctanone Cyclooctanol 24
A cetop h en on e 1-Phenylethanol 65
P ropiophenone 1-Phenylpropanol 70
B enzophenon e Diphenylcarbinol 70
4-M ethyl-2-pentanoneb 4-M ethyl-2-pentanol 37 B enzylidenacetone 4-Phenyl-2-butanone 91 4-Phenyl-2-butanol 4 M esityl oxide 4-M ethyl-2-pentanone 93
B enzaldehyde B enzylalcohol 87
1-Hexanal 1-Hexanol 88
Cinnamic aldehyde 3-Phenylpropanal 8 Cinnamic alcohol 16
C rotonaldehydec Butanal 28
2 -B u te n -l-o l 6 Conditions: carbonyl com pound (10 m m ol), 1,4- butanediol (5 m m ol) R uH C lC O (P P h3)3 (0.03 m m ol), T = 140 °C, Tim e = 20 h; a determ ined by GLC analysis and based on the am ount o f carbonyl com pound used; b dibutyl ether (2 ml) as solvent; c T = 90 °C.
1824 N otizen
ketone to the corresponding alcohol in 60% yield.
Similar observations were reported for hydrogen transfer from 2-propanol to a,/3-unsaturated ketones catalysed by iridium (I) complexes [15].
A m ong aldehydes, benzaldehyde and hexanal were efficiently reduced to primary alcohols. This is not the case with cinnamic aldehyde and croton- aldehyde. Besides low yields of saturated aldehydes and unsaturated alcohols, condensation side pro
ducts were observed. This may be due to the stabil
isation by resonance between C = C and C = 0 bonds and coordination to the metal center as bidentate ligand, blocking the coordination of hydrogen donor.
In separate experim ents, the catalytic activities of ruthenium (II) complexes in the reaction between cyc- lohexanone and 1,4-butanediol have been examined.
Thus after 1 h of the reaction, the extent of reduction decreased in the sequence, R uH C lC O (P P h3)3 (78% ), R uC l2(PPh3)3 (68% ) and R uH ,(P P h3)4 (46% ).
The results obtained here dem onstrate, that stoichiom etric am ounts of 1,4-butanediol can be suc
cessfully explored as hydrogen donors in the catalytic reduction of aldehydes and ketones in bulk without solvent, producing prim ary and secondary alcohols in satisfactory yields.
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