Monohydric Alcohols - American Chemical Society

13

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Monohydric Alcohols in the Flavor and Fragrance Industry J. DORSKY Givaudan Corporation, Research Department, Clifton, NJ 07014

Todays' perfumers and flavorists have a palette of about 5,000 materials at their disposal to formulate the pleasant odors and tasty flavors enjoyed and even demanded in consumer products. Some materials are of natural origin, others are purely synthetic and some are available from both sources, natural and synthetic. Almost all kinds of organic functionalities are represented in the broad palette of the flavorist and perfumer - alcohols, aldehydes, ketones, esters, hydrocarbons, olefins, amines, phenols, heterocyclics, etc. Alcohols are particularly important because they are prominent among the relatively inexpensive and readily available materials which make up the bulk of flavors and especially fragrances. Flavors v s .

Fragrances

F l a v o r s and fragrances are sensory s t i m u l i . Of the two, f l a vors are more complex because they act on the o l f a c t o r y bulb v i a t h e i r v o l a t i l e components and on the t a s t e buds which are s t i m u l a ted by both v o l a t i l e and n o n - v o l a t i l e components. The o v e r a l l r e sponse to a f l a v o r i s a synthesis of the e f f e c t s of both types of components. The response to f r a g r a n c e s , on the other hand, r e s u l t s only from the a c t i o n of v o l a t i l e components. Because f l a v o r s and fragrances f u n c t i o n v i a a common mechanism, many v o l a t i l e materia l s are used f o r both purposes. This i s n i c e l y i l l u s t r a t e d by the perfumers vocabulary f o r fragrance m a t e r i a l s . A c o l l e c t i o n of some 160 words published by a famous perfumer, Ernest S h i f t a n (1) included 75 words u s u a l l y a s s o c i a t e d with f l a v o r s such as almond, bacon, coconut, honey, l i m e , r a s p b e r r y , s p i c y and v a n i l l a . 1

V a r i e t y and D i v e r s i t y of Monohydric A l c o h o l s Givaudan C o r p o r a t i o n , probably the l a r g e s t s u p p l i e r of f l a v o r and fragrance chemicals, o f f e r s about 50 monohydric a l c o h o l s . T h i s i s by no means the whole p i c t u r e . Other s u p p l i e r s o f f e r a d d i t i o n a l a l c o h o l s and some a l c o h o l s are used in-house as i n t e r m e d i a t e s , 0097-6156/81/0159-0197$05.00/0 © 1981 American Chemical Society Wickson; Monohydric Alcohols ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

198

MONOHYDRIC ALCOHOLS

RHODINOL

30%


GERANIOL COEUR

5

CITRONELLOL COEUR

10

PHENYLETHYL ALCOHOL COEUR

10

NEROL COEUR

5

GERAilYL ACETATE

2

ALDEHYDE C-8

10%

ALDEHYDE C-9

13%

4 4

BENZOPHENONE ROSE OXIDE

Figure 1.

Rose base

3.5 17,

•lOSALVA

0.5

ESSENCE OF STYRAX

Z

GUAIACWOOD OIL (GUAIOL)

2

ALDEHYDES

45.0%

ALCOHOLS*

48.0

ESTERS

4.0

ACETALS

0.4

PHENOL ETHERS

0.7

KETONES

0.3

NITROGEN COMPOUNDS

0.5

RESINS

0.1

OTHERS

1.0

PHENYLETHYL ALCOHOL,

Lilac perfume

100%

TOTAL

• HYDROXYCITRONELLAL,

Figure 2.

1

TERPINEOL,

LINALOOL,

ANISIC ALCOHOL,

CIMETIIYLBEilZYL CARBINOL,

CINNAMIC ALCOHOL

Wickson; Monohydric Alcohols ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


13.

DORSKY

Alcohols in the Flavor and Fragrance Industry

199

or are only s o l d i n fragrance mixtures. The number of monohydric a l c o h o l s used by the i n d u s t r y i s no doubt greater than 100. The importance of monohydric a l c o h o l s i n fragrances i s c l e a r l y shown i n the formula f o r a rose base i n Figure 1 which contains 82.5% monohydric a l c o h o l s . The chemistry of some of these a l c o h o l s i s covered l a t e r . A t y p i c a l l i l a c perfume i n Figure 2 contains 48% a l c o h o l s , a l l monohydric. Nature has been very generous i n d i s t r i b u t i n g f r a g r a n t a l c o h o l s among the flowers. Figure 3 l i s t s the number of d i f f e r e n t a l c o h o l s found i n four important f l o r a l e x t r a c t s used i n perfumery: jasmin, h y a c i n t h , ylang-ylang and tuberose. The number ranges from 31 to 56 and terpenoid a l c o h o l s are the most abundant. Conc e n t r a t i o n s of i n d i v i d u a l a l c o h o l s i n e s s e n t i a l o i l s vary widely, from t r a c e s to as much as 80%, i n the case of s a n t a l o l i n sandalwood o i l . Nor has nature neglected to b l e s s f r u i t s with a l c o h o l s which add t h e i r s p e c i a l touch to the f l a v o r s of f r e s h f r u i t . A l i s t of a l c o h o l s found i n apple and banana e x t r a c t s i s shown i n Figure 4. These examples s u f f i c e to show how widely d i s t r i b u t e d a l c o h o l s are i n n a t u r a l f l a v o r s and f r a g r a n c e s . Chemical Types Before the 19th century, perfumers had a t t h e i r d i s p o s a l only n a t u r a l products of p l a n t and animal o r i g i n . Today, perfumers work with about 5,000 m a t e r i a l s , most of which a r e produced synthetically. Among the approximately 100 monohydric a l c o h o l s used, a l l chemical types are represented. Several examples of a l i p h a t i c a l cohols are shown i n Figure 5. Nonyl a l c o h o l and 3-octanol are t y p i c a l f a t t y a l c o h o l s . These a l c o h o l s a r e o f t e n found i n n a t u r a l products but are seldom used because of t h e i r weak odor. In c o n t r a s t , o l e f i n i c a l c o h o l s have strong odors and are widel y used i n perfumes, though a t r e l a t i v e l y low c o n c e n t r a t i o n s . Leaf a l c o h o l has a very pleasant l e a f y , green odor. I t i s found i n many flowers and f r u i t s and i s the most important of the o l e f i n i c alcohols. Commercial l e a f a l c o h o l contains at l e a s t 90% of the c i s isomer. T y p i c a l aromatic a l c o h o l s are shown i n F i g u r e 6. Phenylethyl a l c o h o l i s the most important member of t h i s f a m i l y . I t i s the main c o n s t i t u e n t of French rose and i s a l s o present i n Otto of rose. P h e n y l e t h y l a l c o h o l has a heavy, sweet odor reminiscent of rose petals. I t blends w e l l with other f l o r a l odors and i s widely used i n many f l o r a l fragrances. P h e n y l e t h y l a l c o h o l i s one of the chemi c a l p i l l a r s of perfumery because, i n a d d i t i o n to i t s f i n e odor q u a l i t i e s , i t i s r e l a t i v e l y inexpensive and r e a d i l y a v a i l a b l e . Cinnamic a l c o h o l , a n i s i c a l c o h o l and dimethylphenyl e t h y l c a r b i n o l are other members of the aromatic a l c o h o l f a m i l y .


MONOHYDRIC ALCOHOLS

200


ALIPHATIC

AROMATIC

JASMIN

10

4

HYACINTH

11

YLANG

YLANG

TUBEROSE

Figure 3.

TERPENOID

TOTAL

17

31

12

33

56

10

7

31

48

9

4

21

34

Number of alcohols found in naturalfloralextracts

APPLE

1 - BUTANOL

X

2 - BUTANOL

Alcohols found in fruit extracts

X

X

ETHANOL

X

GERANIOL

X

1 - HEXANOL

X

TRANS-2-HEXEN-I-OL

X

cis-3-HEXEN-l-OL

X

METHANOL

X

2- METHYLBUTAN-1-0L

X

3- METHYLBUTAN-1-0L

X

X

2-METHYLPR0PAN-2-0L

X

X

1 - PENTANOL

X

2 - PENTANOL

Figure 4.

BANANA

X

X

X

1-PR0PAN0L

X

2-PR0PAN0L

X


X

DORSKY

13.

Alcohols in the Flavor and Fragrance Industry FATTY

ALCOHOLS

ODOR CH3(CH2)7CH20H

NONYL

201

FATTY

TYPE

-

ORANGE

ALCOHOL

OH PEPPERMINT-SAGE


CH3CH2^H(CH2)/4CH3

3-OCTANOL

OLEFINIC

CH7CH9

LEAF

\H2CH2OH

ALCOHOLS

GREEN

LEAF

ALCOHOL

cis-3-HEXENOL

r

MUSHROOM

CH3(CH2)/(CH-CH=CH2

VERY

1-0CTEN-3-0L

STRONG

ODOR

Figure 5.

TYPE

CH2CH2OH ROSE-HONEY

PHENYL ETHYL ALCQHQL

CH=CH

CH2OH

Or

BALSAMIC-FLORAL

CINNAMIC AlCOHOI

J3T

FLORAL BALSAMIC

ANISYL ALCOHDI OH ^CHOCH7(!-CHT

© T V

HYACINTH

DIMETHYLPHFNYIFTHVI

Figure 6.

Aromatic alcohols


MONOHYDRIC


202

ALCOHOLS

Terpenoid a l c o h o l s appeared e a r l y i n the h i s t o r y of s y n t h e t i c perfumery because s e v e r a l were r e a d i l y a v a i l a b l e from inexpensive essential o i l s . A l p h a - t e r p i n e o l , c i t r o n e l l o l and l i n a l o o l shown i n Figure 7 are important c o n s t i t u e n t s of pine stump o i l , c i t r o n e l l a o i l and rosewood o i l , r e s p e c t i v e l y . The f o u r t h m a t e r i a l l i s ted, h y d r o x y c i t r o n e l l a l , i s a hydroxy aldehyde which perhaps has a questionable place i n t h i s d i s c u s s i o n . I t i s included because i t i s one of the most important fragrance chemicals used today. "Hydroxy" i s almost a perfume unto i t s e l f . I t s s o f t flowery, l i n d e n blossom odor blends very w e l l i n many f l o r a l perfumes. Sesquiterpenic a l c o h o l s used i n perfumery are mainly of natural origin. Three a l c o h o l s of t h i s type are shown i n Figure 8. Cedrol i s the main a l c o h o l c o n s t i t u e n t of cedarwood o i l . Alphas a n t a l o l c o n s t i t u t e s about 80% of sandalwood o i l and about 30% p a t c h o u l i a l c o h o l i s found i n p a t c h o u l i o i l , a very popular woodyearthy fragrance m a t e r i a l . Ethyl Alcohol Perfumes, colognes and t o i l e t waters are s o l u t i o n s of perfume o i l s i n s p e c i a l l y denatured a l c o h o l s , ( e t h y l a l c o h o l with v a r i o u s denaturants which make i t u n s u i t a b l e f o r human consumption). In a d d i t i o n , ethanol i s used as a solvent f o r f l a v o r s , as an e x t r a c t i o n solvent f o r many n a t u r a l products and as a reagent f o r the production of many e t h y l e s t e r s . Summing up a l l these uses, the q u a n t i t y of ethanol used i n the fragrance and f l a v o r i n d u s t r y tops a l l other a l c o h o l s by f a r . Perfumes c o n t a i n 10-25% o i l i n SDA 39C. The denaturant i s d i e t h y l phthalate - 1:100. Colognes and t o i l e t waters c o n t a i n 26% o i l i n SDA 40 as shown i n F i g u r e 9. The denaturant i s brucine s u l f a t e - 3 oz. per 100 g a l l o n s . Ethanol used as a solvent f o r f l a v o r s i s the 95% grade and i s f u l l y taxed s i n c e i t i s potable. A l l ethanol used f o r fragrances and f l a v o r s must get by the c l o s e s c r u t i n y of the Q u a l i t y C o n t r o l perfumer or f l a v o r i s t . The road can be rough. Hydroxycitronellal T h i s i s probably the s i n g l e most important m a t e r i a l used by the fragrance i n d u s t r y . Several m i l l i o n pounds are used annually, mainly i n soaps and detergents. The p r i n c i p a l method of manufacture shown i n Figure 10 i s by h y d r a t i o n of c i t r o n e l l a l v i a the b i s u l f i t e a d d i t i o n product (2). The aldehyde moiety must be p r o t e c ted before h y d r a t i o n . A second manufacturing process s t a r t s with c i t r o n e l l o l which i s hydrated under a c i d c o n d i t i o n s . The primary a l c o h o l end of the molecule i s then dehydrogenated c a t a l y t i c a l l y or by o x i d a t i o n to the aldehyde.


13.


DORSKY

203

ODOR TYPE LILAC .OH ALPHA-TERPINEOL

^CHoOH


FRESH - ROSEY

CITRONELLOL

FLORAL - WOODY

LINALOOL ;HO

LILY-OF-THE-VALLEY

HYDROXYCITRONELLAL

Figure 7.

"Terpenoid" alcohols

Figure 8.

Sesquiterpene alcohols

CEE-ROL

-CHoQH

ALPHA-SANTALOL

PATCHOULI

ALCOHOL


MONOHYDRIC ALCOHOLS


204

PERFUME

10-25?

COLOGNE/TOILET

Figure 9.

Ethyl alcohol

OIL

IN 9 5 % 39C ALCOHOL

WATER

2-6% OIL

IN

f.?-?.os w

OH

Figure 10. Hydroxycitronellal


ALCOHOL

13.

DORSKY


205


Menthol Peppermint f l a v o r and " c o o l " c i g a r e t t e s owe t h e i r d i s t i n c t i v e f l a v o r character to 1-menthol, a secondary a l c o h o l and another multimillion-pound product of the i n d u s t r y . Pure 1-menthol i s used mainly f o r f l a v o r i n g c i g a r e t t e s and much of t h i s m a t e r i a l i s i s o l a t e d from the Mentha a r v e n s i s p l a n t . Substantial quantities are a l s o produced s y n t h e t i c a l l y from meta-cresol as shown i n F i g ure 11. I s o p r o p y l a t i o n y i e l d s a mixture of isomers from which thymol i s i s o l a t e d . Hydrogenation of thymol gives a mixture of menthol isomers. Racemic menthol i s recovered from the mixture by c a r e f u l f r a c t i o n a t i o n o f menthol as an e s t e r . 1-Menthol i s the d e s i r e d isomer because i t i s r e s p o n s i b l e f o r the c o o l i n g e f f e c t . Several p r a c t i c a l methods have been described f o r separating the 1-isomer. One patented by Haarmann and Reimer i s e s p e c i a l l y i n t r i g u i n g (3). A supersaturated s o l u t i o n of racemic menthol e s t e r s i s seeded with the 1-ester which then s e l e c t i v e l y c r y s t a l l i z e s . Geraniol/Citronellol These " r o s e " a l c o h o l s were formerly obtained from c i t r o n e l l a o i l as a 2:1 mixture of g e r a n i o l / c i t r o n e l l o l . High p u r i t y c i t r o n e l l o l was obtained by hydrogenation of the mixture. Soap perfumery was h i g h l y dependent on cheap n a t u r a l g e r a n i o l / c i t r o n e l l o l . Since the 1960 s, s y n t h e t i c g e r a n i o l has been a c o n t r o l l i n g f a c t o r i n the market f o r these a l c o h o l s . The s y n t h e t i c route i s shown i n Figure 12. Myrcene, produced by p y r o l y s i s of beta-pinene, i s conv e r t e d to a mixture of g e r a n i o l and n e r o l , i t s c i s isomer, f i r s t by r e a c t i o n w i t h HC1, then with sodium acetate and f i n a l l y w i t h sodium hydroxide to saponify the e s t e r s . Commercialization o f t h i s chemistry by Glidden (4) was the f i r s t case where synthesis freed the i n d u s t r y from t o t a l dependence on a n a t u r a l source of a major product. f

Linalool In the mid-1950's, Hoffmann La-Roche o f f e r e d s y n t h e t i c l i n a l o o l and i t s e s t e r s to the fragrance i n d u s t r y (5). This was another r e v o l u t i o n a r y step i n the replacement of n a t u r a l products w i t h s y n t h e t i c s . L i n a l o o l was an intermediate i n Roche's manufacture of s y n t h e t i c i s o p h y t o l f o r Vitamin E. For s e v e r a l years perfumers were r e l u c t a n t t o use chemically pure s y n t h e t i c l i n a l o o l and i t s e s t e r s i n place o f m a t e r i a l s i s o l a t e d from e s s e n t i a l o i l s . F i n a l l y , economics p r e v a i l e d and today the amount of s y n t h e t i c l i n a l o o l and i t s e s t e r s used f a r exceeds the t r a d i t i o n a l " l i n a l o o l rich" essential o i l s . Worldwide, i n excess of f i v e m i l l i o n pounds of l i n a l o o l and i t s e s t e r s are manufactured f o r fragrances by f i v e d i f f e r e n t processes. Three of them i n v o l v e methylheptenone as an intermediate. The other two a r e based on t u r p e n t i n e . The three routes t o methylheptenone a r e o u t l i n e d i n Figure 13.



MONOHYDRIC ALCOHOLS

Figure 11. Menthol

Figure 12. Geraniol/citronellol


13.

DORSKY

Alcohols

in the Flavor

and Fragrance

Industry

207


In the f i r s t route, methylbutenol i s made from acetone and acetylene followed by hydrogenation. Reaction with methyl i s o p r o penyl ether y i e l d s methylheptenone (6). The second route i n v o l v e s the r e a c t i o n of i s o b u t y l e n e , formaldehyde and acetone (7). Methyl v i n y l ketone i s an intermediate. F i n a l l y , methylheptenone i s made by a l k y l a t i o n of acetone with p r e n y l c h l o r i d e which i s d e r i v e d from isoprene (8). The i n i t i a l product i s the t e r m i n a l o l e f i n which i s isomerized to the d e s i r e d i s o p r o p y l i d e n e compound. As shown i n Figure 14, l i n a l o o l i s obtained by e t h y n y l a t i o n of methylheptenone, followed by hydrogenation. Sandalore Some of the chemistry developed by the i n d u s t r y more r e c e n t l y , to produce new monohydric a l c o h o l s , i s j u s t as i n t e r e s t i n g as the l i n a l o o l chemistry. Sandalore, a recent new Givaudan chemical with a p e r s i s t e n t , sandalwood odor i s made according to the scheme i n F i g u r e 15 09). Alpha-pinene, the s t a r t i n g m a t e r i a l , i s converted to the epoxide which i s c a t a l y t i c a l l y rearranged to campholeni c aldehyde. A l d o l condensation with methyl e t h y l ketone followed by hydrogenation y i e l d s Sandalore®. Phenylethyl A l c o h o l T h i s important fragrance m a t e r i a l probably was introduced i n commercial perfumery during the f i r s t decade of the twentieth century with the d i s c o v e r y of the Bouveault-Blanc r e d u c t i o n of e s t e r s by sodium and an a l c o h o l (10). T h i s i s the f i r s t of s e v e r a l methods of p r e p a r a t i o n shown i n F i g u r e 16. Large q u a n t i t i e s of phenyle t h y l a l c o h o l were made by sodium r e d u c t i o n of b u t y l phenylacetate i n normal butanol. The b a s i c raw m a t e r i a l s were r e a d i l y a v a i l a b l e at low c o s t from benzyl c h l o r i d e , sodium cyanide and fermentation butanol. T h i s process was superceded by the F r i e d e l - C r a f t s r e a c t i o n of benzene and ethylene oxide which i s now the most important commerc i a l process (11). Cheap ethylene oxide brought about t h i s s h i f t . For a short time, commercial q u a n t i t i e s of p h e n y l e t h y l a l c o h o l were made by the Grignard r e a c t i o n of phenyl magnesium c h l o r i d e on ethylene oxide but t h i s process could not compete with the F r i e d e l Craf ts process. More r e c e n t l y , low cost styrene oxide has been considered as a s t a r t i n g m a t e r i a l . C a t a l y t i c hydrogenation under c o n t r o l l e d c o n d i t i o n s y i e l d s high q u a l i t y p h e n y l e t h y l a l c o h o l (12). Unfortun a t e l y , low cost styrene oxide never m a t e r i a l i z e d i n t h i s country; consequently, l i t t l e p h e n y l e t h y l a l c o h o l has been manufactured by t h i s route. The four methods of producing p h e n y l e t h y l a l c o h o l depicted i n Figure 16 i l l u s t r a t e the dependence of the fragrance i n d u s t r y on the organic chemical i n d u s t r y . Most l a r g e volume products used i n



208 MONOHYDRIC ALCOHOLS

Figure 14.

Linalool


DORSKY

Alcohols

in the Flavor

and

Fragrance

Industry


13.


209

MONOHYDRIC


210

ALCOHOLS

perfumes a r e commodity items that must be made by the l e a s t expens i v e process. Very o f t e n , raw m a t e r i a l s cost determines which process w i l l p r e v a i l . T h i s overview of monohydric a l c o h o l s covered the major products used by the i n d u s t r y . The one exception was Sandalore which was introduced only r e c e n t l y . I t was included as an example of the c o n t i n u i n g search f o r new fragrance m a t e r i a l s to r e p l a c e natur a l p r o d u c t s , i n t h i s case, expensive and scarce sandalwood o i l . I t i s hoped that a s i m i l a r review i n f i v e years would i n c l u d e Sand a l o r e or another major new, s y n t h e t i c fragrance a l c o h o l .

Abstract Monohydric alcohols are found in great variety in natural flavor and fragrance materials. Many chemical types are represented: aliphatic, alicyclic, polycyclic, heterocyclic, terpenoid, saturated, unsaturated, etc. In flavor and odor they cover practically the entire useful spectrum. Some are present in low concentrations and others are the principal components of the natural products. Flavorists and perfumers first formulated sophisticated flavors and fragrances using naturally occurring alcohols. As the art and science progressed, chemists devised synthetic routes to many of the important natural alcohols and produced them cheaper and in higher quality. Commercial synthesis of some natural alcohols, such as, geraniol, citronellol, menthol and linalool has had a very significant impact on the economics of the flavor and fragrance industry. The preparation and use of the more important monohydric alcohols is reviewed. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Shiftan, E . , Encyclopedia of Chemical Tech., 2nd Ed., John Wiley & Sons, New York, 1967, 14, 744. Meuly, W.C., U.S. Pat. 2,235,840, March 25, 1941. Haarman & Reimer, GMBH, Brit. Pat. 1,369,714, October 9, 1974. Webb, R.L., U.S. Pat.- 3,031,442, April 24, 1962. Offner, A., Soap, Perfumes, Cosmetics, February 1965, 38, 125. Saucy, G. and Marbet, R., Helv. Chim. Acta., 1967, 50, 2091. Pommer, H., Müller, H. and Overwien, H., Ger. Pat. 1,259,876, May 11, 1966. Ger. Pat. 1,268,135, July 16, 1966. Meuly, W.C., Riechstoffe, Aroman, Korperpflegemittel, 1972, 6, 191. Naipawer, R.E. and Easter, W., U.S. Pat. 4,052,341, October 4, 1977. Bouveault, L. and Blanc, G., Compt. Rend., 1903, 136, 1676, Bull. Soc. Chim. France, 1904, 31 (3) 666. Carpenter, S., U.S. Pat. 2,013,710, 1935. Wood, T.F., U.S. Pat. 3,579,593, May 18, 1971.

RECEIVED

December 29, 1980.


Monohydric Alcohols - American Chemical Society

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