Feb. 20, 1957
UNSATURATED ALDEHYDE DIMETHYL ACETALS
889
centration was estimated on the basis of equation 10, to give an approximate value of 2 X 1.2 mole-2 set.-' for k4 a t 30'. Values for the rate constants kz and ka were obtained a t 10, 20, 30 and 40'. These results are summarized in Table IV along with the energies of
mide as a nucleophilic agent which have been assumed in the explanations used here have been suggestedg as possible for carbon-carbon double bonds substituted with electron-withdrawing groups. Kinetic data for the addition of bromine to such unsaturated compounds in the presence of halide ions have been interpreted as showing that TABLE IV either a polyhalide ion is involved in a nucleophilic SUMMARY OF THE RATECONSTANTS AT VARIOUS TEMPERA-attack on the double bondlo or a halide ion and TURES AND OF THE ENTHALPIES AND ENTROPIES OF ACTIVA- bromine are involved, in a concerted TION I n no case reported has this type of trihalideTemp., olefin interaction been as well defined as it is in the 'C. Equation 2' Equation 3 b present case. Of course, the reaction given in k" 10 (2.6 f 0.2)lO-2 (0.86 f 0.01)10-6 3 might just as well have been interequation kc 20 ( 4 . 3 f .4)10-2 (2.2 f .1)10-6 preted as a concerted action of bromine and brokc 30 (9.9 f .3)10-2 (6.7 =k .2)10-6 mide on crotonic acid as far as the kinetic results k" 40 (13.8 f 1.2)lO-* (14.3 f .4)10-6 were concerned. This type of behavior of polyA H * , kcal. . . 10.6 16.1 halides is t o be contrasted with that observed12 A S h , e.u. 30 -28.2 -24.6 a The units of kz are 1.2 mole-$ sec.'. The units of ka are for tribromide ion which reacted much more slowly 1. mole-' set.-'. c The measure of the precision is the than bromine in the addition of trans-stilbene in standard deviation of the average values used. methanol. (9) P. B. D. de la Mare, Qxarl. Reus., 3, 126 (1949). activation and entropies of activation calculated (10) P. B.D.de la Mare and P. W. Robertson, J. Chem. Soc., 2838 from them. The relatively high negative values (19501, and the references which they give. obtained for the entropies of activation are con'11) K.Nozaki and R . A. O g g , Jr., THISJ O U R N A L , 64,697,704, 709 sistent with a highly ordered transition state for (1942). (12) P. D. Bartlett and D. S. Tarbell. i b i d . , 68, 466 (1936). each reaction. Such actions of quaternary ammonium tribro- IOWA CITY,IOWA
[CONTRIBUTION FROM
THE
RESEARCH LABORATORY OF COMPAGNIE PARENTO, INC.]
Preparation of cr,P-Unsaturated Aldehyde Dimethyl Acetals and their Free Aldehydes BY PAUL 2. BEDOUKIAN RECEIVED JULY 11, 1956 Elimination of hydrogen bromide from the a-bromoacetals of the fatty aldehydes (C-7 to C-12) gave the acetals of the corresponding a,P-unsaturated aldehydes. The free aldehydes were obtained from the acetals by acid hydrolysis. A study was made of the odor properties of these compounds. The physical properties of the enol acetates and bromoaldehyde dimethyl acetals of the saturated aldehydes are reported.
This investigation was carried out for the purpose of determining the odor characteristics of the acetals of a,@-unsaturatedfatty aldehydes (C-7 to C-12) as well as those of the free aldehydes. The saturated fatty aldehydes of this series play an important role in perfume compositions and are extensively used in perfumes, cosmetics and soaps. The preparation of a,P-unsaturated aldehydes has presented considerable difficulties and involved indirect and lengthy procedures. The present method, although i t does not give high overall yields, is very convenient and is generally applicable to the conversion of any saturated aldehyde, possessing an a- and 0-hydrogen, to its a,@-unsaturatedanalog. The following reactions are used in preparing a,@-unsaturated aldehydes : The saturated aldehyde is converted to the enol acetate and then brominated in carbon tetrachloride. On adding methanol to the brominated mixture, the dimethyl acetal of a-bromoaldehyde is obtained in good yields. The latter on treatment with potassium hydroxide in butanol gives the unsaturated acetal which is converted to the free a,@-unsaturated aldehyde by acid hydrolysis.
The preparation of the a-bromoaldehyde dimethyl acetal of heptaldehyde has been reported.' RCHzCHzCHO
+ AczO(KAc)
--.)
RCHzCH=CHOCOCH,
MeOH RCH2CHBrCH(OMe)z tRCHzCHBrCHBrOCOCHa
4
KOH (in B ~ O H ) RCH=CHCH(OMe)z
acid --f
RCH=CHCHO
Identical procedures were used in the preparation of the bromoacetals of higher aldehydes. None of the acetals of the a,&unsaturated aldehydes (C-7 to C-12) has been reported previously. All of the free aldehydes have been prepared by various methods but no comments have been made on their odor properties. 2-Heptenal has been prepared by the chromic (1) P. 2. Bedoukian, THIS JOURNAL, 66, 1325 (1944); P.Z.Bedoukian, "Organic Syntheses," Coll. Vol. 111, John Wiley and Sons,Inc., N e w York, N. Y., p. 127.
PAUL2. BEDOUKIAN
890
VOl. 79
TABLE I YIELDSAND PHYSICAL PROPERTIES OF THE ENOLACETATES, CY-BROMO ALDEHYDEDIMETHYL ACETALS, CY,P-UNSATURATED DIMETHYL ACETALS AND a,@-UNSATURATEDALDEHYDES (e-7 TO c-12) Heptanal
Pure enol acetate from aldehyde
Yield, % B.p. (mm.) ?ZZZD d22u
Octanal
Konanal
Undecanal
Decanal
Dodecanal
47 42 39 46 34 37 95-97 (17) 110-112 (17) 126-128 (16) 133-135 (16) 111-113(3) 88-90 (17) 1.4420 1.4390 1.4374 1.4300 1.4350 1.4350 0.883 0.895 0.885 0.895 0.895 0.887 78 86 83 72 85 81 117-119 (17) 140-142 (26) 146-148 (23) 155-157 (17) 137-139 (4) 151-153 (4) 1.4540 1.4552 1.4552 1.4524 1.4532 1.4530 1.100 1.085 1.120 1.152 1.135 1.195 55 51 55 58 52 34 95-97 (2) 73-75 (13) 100-102 (16) 123-125 (18) 92-94 (2) 66-68 (11) 1.4357 1.4372 1.4338 1.4332 1.4308 1.4240 0.874 0.868 0.860 0.883 0.866 0.876 45 40 62 64 62 58 59-61 (18) 78-80 (9) 98-100 (12) 117-119 (22) 115-117 (10) 125-128 (10) 1.4320 1.4220 1.4240 1.4482 1.4408 1,4442 0.865 0.854 0.860 0.843 0.853 0.854
or-Bromoaldehyde Yield, % dimethyl acetal B.p. (nim.) from enol ace#D d "25 tate a,,%Unsaturated Yield, % aldehydedimethyl B.P. (mm.) acetal from nZzD bromoacetal d22u or,@-Unsaturated Yield, % ' aldehydefromun- B.p. (mm.) saturated acetal +D (slight acetal dZ2U impurities) Semicarbazone, m.p., "C. 174' 2,4-Dinitrophenylhydrazone, m.p., "C. 133O
172*
167'
165d
164"
160/
111 Melting points reported in the literature: 16Q02. 179"'. * 163".10 163'8; 160-161°.11 168"; 167-1G8°13; 124.4-12503; 126°.12 i 128.8"13. 168.5"14; 162O.20 e 161.5-162.5".1a f 165.5-166°14; 15G.24 131.5O.8 121-123O.6 122.6".13 122h
127'
128'
123'
ANALYSES OF INTERMEDIATES Compound
Mol. wt.
Heptenal dimethyl acetal Octanal enol acetate Octenal dimethyl acetal Bromooctanal dimethyl acetal Nonanal enol acetate Nonenal dimethyl acetal Bromononanal dimethyl acetal Decanal enol acetate Decenal dimethyl acetal Bromodecanal dimethyl acetal Undecanal enol acetate Undecenal dimethyl acetal Bromoundecanal dimethyl acetal Dodecanal enol acetate Dodecenal dimethyl acetal Bromododecanal dimethyl acetal 2,4-Dinitrophenylhydrazone of dodecenal
158.25 170.26 172.28 253.15 184.26 186.28 267.18 198.26 200.27 281.18 212.26 214.27 295.18 226.26 228.27 309.18 364.45
ODORSOF
THE
Adduct formula
Carbon, % Calcd. Found
68.14 CoHiaOz 70.48 CioHisOz 69.65 CioHzoOe 47.40 CloHzlOtBr 71.63 CnHaOz 70.85 CiiHaOz 49.40 C11HzaOzBr 72.63 Ci2HaOz 71.89 CizHuOz 51.21 ClzHzaO~Br 73.49 C13H2402 72.80 CiaHz60z C I I H Z ~ O Z B ~ 52.85 74.25 C14H2602 73.59 Cl4H2802 54.36 C14HzoOzBr 59.27 Cl8HpsO4P\T4
68.13 69.72 68.92 48.39 70.59 70.71 49.80 72.66 70.46 52.66 T3.33 72.47 53.31 73.91 72.34 54.67 58.14
Hydrogen, % Calcd. Found
11.40 10.64 11.68 8.37 10.93 11.89 8.70 11.17 12.07 8.97 11.45 12.22 9.22 11.58 12.36 9.44 7.74
11.17 10.37 11.84 8.36 10.95 11.79 8.70 11.14 11.86 9.09 11.50 12.17 9.50 11.59 11.31 10.59 7.31
CGP-UNSATURATED ACETALS ASD THEIRALDEHYDES Dimethyl acetal
Aldehyde
Strong grassy green odor More pungent and greener than heptaldehyde 2-Heptenal Strong and not unpleasant, grassy odor Grassy odor, coarser and more powerful than octanal 2-Octenal Pleasant fatty green odor, not strong 2-Nonenal Less pleasant than nonanal and more pungent and powerful 2-Decenal Less pleasant and greener than decanal Weak fatty odor Very weak sweet fatty odor Strong odor similar to undecanal 2-Undecenal Very weak fatty note 2-Dodecenal Weaker than dodecanal Odor observation tests were made on 10% and 2% ethanol solutions as well as on the full strength material.
acid oxidation of the corresponding a l c ~ h o land ~ . ~ the oxidation of 1-octene with cobalt acetate,&by dehydration of 1,4-heptanedio14; 2-octenal, by the action of allyl methyl ether on hexaldehyde in the presence Of boron fluoride6 and by the chromic (2) R . Delaby and S. Guillot-Allegre, Compt. rcnd., 192, 1467 (1931). (3) C. J. Martin, A. I. Schepartz and B. P.Daubert, THISJOURNAL, 10, 2601 (1948). (4) hl. Gouge. A ~ z n
