Process for producing 2-mercapto-1,4-diones

BACKGROUND OF THE INVENTION
The present invention relates to novel processes for producing 3-mercaptoalkane-1,4-diones.
Artificial flavoring agents for foodstuffs have received increasing attention in recent years. In many areas, such food flavoring agents are preferred over natural flavoring agents at least in part because of the uniform flavor that may be so obtained. For example, natural food flavoring agents such as extracts, essences, concentrates and the like are often subject to wide variation due to changes in the quality, type and treatment of the raw materials. Such variation can be reflected in the end product and results in unreliable flavor characteristics and uncertainty as to consumer acceptance and cost. Additionally, the presence of the natural product in the ultimate food may be undesirable because of increased tendency to spoil. This is particularly troublesome in convenience and snack food usage where such products as dips, soups, chips, prepared dinners, canned foods, sauces, gravies and the like are apt to be stored by the consumer for some time prior to use.
The fundamental problem in preparing artificial flavoring agents is that of achieving as nearly as possible a true flavor reproduction. This generally proves to be a difficult task since the mechanism for flavor development in many foods is not understood. This is notable in products having meaty and roasted flavor characteristics. It is also notable in products having vegetable-like and hydrolyzed vegetable protein-like and anise-like flavor characteristics
Reproduction of roasted and meat flavors and aromas and vegetable-like and hydrolyzed vegetable protein-like and anise-like flavors and aromas has been the subject of the long and continuing search by those engaged in the production of foodstuffs. The severe shortage of foods, especially protein foods, in many parts of the world has given rise to the need for utilizing non-meat sources of proteins and making such proteins as palatable and as meat-like as possible. Hence, materials which will closely simulate or exactly reproduce the flavor and aroma of roasted meat products and liver products and vegetable products are required.
Moreover, there are a great many meat containing or meat based foods presently distributed in a preserved form. Examples being condensed soups, dry-soup mixes, dry meat, freeze-dried or lyophilized meats, packaged gravies and the like. While these products contain meat or meat extracts, the fragrance, taste and other organoleptic factors are very often impaired by the processing operation and it is desirable to supplement or enhance the flavors of these preserved foods with versatile materials which have either roasted meat or gravy-like or vegetable-like or meat-like or ham-like nuances.
2-Alkylfuran-3-thiols and bis (alkyl-3-furyl) disulfides are disclosed in U.S. Pat. No. 3,723,475 issued on Mar. 27, 1973 to supply meaty flavor aroma and taste nuances to foodstuffs. 2-Thia-substituted-1,4-diones are disclosed in U.S. Pat. No. 3,836,563 issued on Sept. 17, 1974 to also supply meaty flavors to foodstuffs.
Swiss Pat. No. 531,313 discloses the addition of hydrogen sulfide across a double bond, eliminating the double bond.
Such a reaction, however, is not shown in conjunction with a chemical compound which has two ketone moieties.
The mechanism of the addition of hydrogen sulfide across a double bond of an alpha-beta-unsaturated ketone is set forth at lines 40-67 of columns 3 and 4 of Swiss Pat. No. 531,559. The formation of thio esters using thio acetic acid and unsaturated ketones is set forth at lines 15-20 of column 6 of Swiss Pat. No. 531,559.
U.S. Pat. No. 2,630,452 to Crouch, et al discloses processes for reacting unsaturated nitriles with thio acids whereby the thio ester moiety adds to the double bond at the "alpha" position with respect to the CN moiety using an aqueous alkali metal hydroxide catalyst or a quaternary ammonium compound catalyst. The substance of Crouch, et al may be illustrated by the following reaction between acrylonitrile and thioacetic acid: ##STR4## At column 2, lines 40-45, Crouch, et al states: "In accomplishing the thioacetic acid-acrylonitrile reaction, it has been found to be highly advantageous to employ certain basic catalysts as reaction promoters and directors. The preferred catalyst is a quaternary ammonium compound designated by the general formula . . . "
In example IV of Crouch, et al, acrylonitrile is reacted with thioacetic acid in the presence of a t-butyl hydroperoxide catalyst at a temperature of 43.degree.-49.degree. C.
U.S. Pat. No. 3,441,589 to Oswald discloses reaction of thiol compounds such as mercaptans and thiolcarboxylic acids being selectively added to esters which, in turn, are formed by the reaction of maleic acid, fumaric acid or maleic anhydride with terminally unsaturated alcohols such as allyl alcohol at either of the terminal double bonds of the ester functionality or at the maleic or fumaric side of unsaturation with the use of either free radical or ionic catalysts. At column 7, Example 8, Oswald teaches the reaction of diallyl maleate with thiolacetic acid to form n-(3-acetylthio)-propyl allyl maleate according to the following reaction: ##STR5## in the presence of a free radical catalyst, such as ultraviolet light or gamma radiation or a "wide variety of peroxidic and azo compounds" (see column 3, lines 60-62).
Reid "Organic Chemistry of Bivalent sulfur", Volume IV, 1962, Chemical Publishing Co., Inc.; discloses reactions of thioacetic acid with unsaturated compounds. At pages 15 and 16 Reid states:
"The most interesting reaction of thioacetic acid is its ready addition to unsaturates. An example of this is its addition to acrylonitrile. In this it exhibits its mercaptan character but in acitivity it far surpasses most mercaptans. Usually the addition takes place spontaneously and completely. With styrene the reaction is: ##STR6## The product is the beta-phenethyl ester of thioacetic acid and is identical with that from phenethyl mercaptan and acetyl chloride . . . "
Hydrolysis of a thio ester to a thiol is set forth at page 446 of chapter 36 of "Organic Sulfur Compounds " Volume 1, Editor: N. Kharash, Pergamon Press 1961 London.
No teaching exists in the prior art to show that, given the structure: ##STR7## where R.sub.2 is lower alkyl and R.sub.1 is hydrogen, the effect of carrying out a reaction of a 2-ene-4-one-1-al with a thioacid (in the presence of base) is directive leading substantially to a reaction product where the thioester substitution is alpha to the ketone moiety and not the aldehyde moiety.
Furthermore, given the 2-ene-1,4-dione reactants of our invention, there is no prediction in the prior art that either (i) no catalyst is necessary in the case of using a hex-3-ene-2,5-dione reactant, or (ii) a basic catalyst is needed and the addition is directive in the case of using a pent-2-ene-4-one-1-al.
THE INVENTION
The processes of the present invention provide straight-forward methods for producing 3-mercaptoalkane-1,4-diones in good yields in an economical manner.
Briefly, the processes of our invention comprise the steps of:
i. Providing a 2-ene-alkane-1,4-dione having the structure: ##STR8##
ii. Intimately admixing said 2-ene-alkane-1,4-dione with a sulfur compound having the formula:
R.sub.3 SH
thereby providing a substituted or unsubstituted 2-thia substituted-1,4-dione having the structure: ##STR9## iii. Hyrdolyzing said 2-thia substituted-1,4-dione to form a 2-mercapto alkane-1,4-dione having the structure: wherein R.sub.3 is selected from the group consisting of acyl and aroyl, wherein R.sub.2 is lower alkyl; and wherein R.sub.1, R.sub.4 and R.sub.6 are the same or different and are each selected from the group consisting of hydrogen and lower alkyl; wherein when R.sub.1 is hydrogen, the reaction is carried out in the presence of an organic base; and wherein when R.sub.1 is lower alkyl, the reaction is carried out in the absence of catalyst.
Two particularly novel features of our invention involve (i) addition of the thiol acids, either ##STR10## to a hex-3-ene-2,5-dione, e.g., having the structure: ##STR11## at room temperature in the absence of any catalyst to produce economic yields of 2-thia substituted alkane-1,4-dione, e.g., having the structure: ##STR12## and (ii) addition of a thiol acid, either ##STR13## to pent-2-ene-4-one-1-als, e.g., having the structure: ##STR14## in the presence of an organic base to yield a 3-thia substituted pentane-4-one-1-al, e.g., having the structure: ##STR15## the addition being directive to that carbon atom (originally having the C=C double bond) which is alpha to the carbonyl group of the ketone moiety rather than the aldehyde moiety.
Examples of thio acids useful in our process are:
thioacetic acid
thiopropionic acid
thiobutyric acid
thioisobutyric acid
thio-n-pentenoic acid
thiocinnamic acid
thiobenzoic acid
2-methyl-thiobenzoic acid
3-methyl-thiobenzoic acid
4-methyl-thiobenzoic acid
2,4-dimethyl-thiobenzoic acid
3,5-dimethyl-thiobenzoic acid
Whether an organic base is used or not in the reaction with the 2-ene-1,4 dione with the thio acid having the formula R.sub.3 SH, the 2-ene-1,4 dione can be exemplified as follows:
______________________________________CompoundName R.sub.1 R.sub.2 R.sub.4______________________________________3-Hexen-2,5-dione Methyl Methyl Hydrogen3-Methyl-3-hexen- Methyl Methyl Methyl2,5 dione3-Methyl-3-hepten- Methyl Ethyl Methyl2,5 dione3-Ethyl-3-hepten- Methyl Ethyl Ethyl2,5 dione4-Ethyl-4-octen- Ethyl Ethyl Ethyl3,6 dione3-Propyl-3-hepten- Methyl Ethyl Propyl2,5 dione4-Methyl-3-hepten- Ethyl Methyl Methyl2,5 dione4-Methyl-4-octen- Ethyl Ethyl Methyl3,6-dione4-Methyl-4-nonen- Ethyl Propyl Methyl3,6-dione4-Propyl-3-hepten- Ethyl Methyl Propyl3,6-dione5-Methyl-5-decen- Propyl Propyl Methyl4,7-dione5-Methyl-4-nonen- Propyl Ethyl Methyl3,6-dione4-Methyl-3-nonen- Butyl Methyl Methyl2,5-dione4-Ethyl-3-nonen- Butyl Methyl Ethyl2,5-dione3-Methyl-3-nonen- Methyl Butyl Methyl2,5-dione3-Propyl-3-nonen- Methyl Butyl Propyl2,5-dione3-Butyl-3-hexen- Methyl Methyl Butyl2,5-dione4-Octen-3,6-dione Ethyl Ethyl Hydrogen______________________________________
As stated above, R.sub.1 and/or R.sub.2 can be hydrogen for the purposes of these processes of our invention in the event that in the reaction of the 2-ene-1,4 dione with the thioacid of the formula R.sub.3 SH, an organic base is used. Hence, in addition to the foregoing compounds, the following compounds can be utilized in the reaction with R.sub.3 SH:
______________________________________CompoundName R.sub.1 R.sub.2 R.sub.4______________________________________2-Buten-1,4-dial Hydrogen Hydrogen Hydrogen2-Methyl-2-buten- Hydrogen Hydrogen Methyl1,4-dial2-Pentenal-4-one Methyl Hydrogen Hydrogen2-Hexenal-4-one Ethyl Hydrogen Hydrogen3-Methyl-2-hexenal Ethyl Hydrogen Methyl4-one2-Methyl-2-pentenal Hydrogen Hydrogen Methyl4-one2-Methyl-2-heptenal Hydrogen Propyl Methyl4-one2-Methyl-2-octenal Hydrogen Butyl Methyl4-one______________________________________
Examples of useful organic bases are piperidine, pyridine, quinoline, triethyl amine and alpha-picoline.
The reaction may be carried out in a solvent such as water or an ether such as diethyl ether or a hydrocarbon such as benzene or hexane or cyclohexane. The reaction may also be carried out without the use of a solvent. The reaction may be carried out under reflux conditions although temperatures varying from 0.degree.up to 60.degree. C are suitable and will give rise to commercially suitable yields. When the reaction is carried out with highly volatile reactants, higher pressures than atmospheric pressure are preferred, e.g., 3 atmospheres pressure. Examples of reaction products, 3-thia-substituted-1,4-diones which are formed from the reaction of the 2-ene-1,4-diones with the thioacids, having the formula R.sub.3 SH are as follows:
______________________________________ 3-Thia Substituted2-ene-1,4-dione R.sub.3 SH 1,4-dione ReactionReactant Reactant Product______________________________________3-Hexen-2,5-dione Thioacetic acid 3-Thioacetyl-2,5- hexan-dione3-Methyl-3-hexen- Thiopropionic 3-Thiopropionyl-4-2,5-dione acid methyl hexan-2,5- dione3-Methyl-3-hepten- Thiobenzoic acid 4-Thiobenzoyl-4-2,5-dione methyl heptan-3,6- dione4-Ethyl-4-octen- Thioacetic acid 4-Thioacetyl-5-ethyl-3,6-dione octan-3,6-dione2-Buten-1,4-dial Thioacetic acid 2-Thioacetyl-butan- 1,4-dial2-Pentenal-4-one 4-Methyl-thio 3-Thiobenzoyl-pentenal- benzoic acid 4-one2-Pentenal-4-one Thioacetic acid 3-Thioacetyl-pentanal- 4-one______________________________________
The compounds having the structure: ##STR16## are then hydroylzed first using a weak base (e.g., 2-5% aqueous NaOH, LiOH or KOH) and then neutralizing with acid to a pH of 5-6 to form compounds having the structure: ##STR17## which have useful organoleptic properties. Thus, for example, 3-thioacetyl-2,5-hexanedione is hydrolyzed to 3-mercapto-2,5-hexanedione by treating the 3-thioacetyl compound first with 2% aqueous NaOH and then adjusting the pH to about 5 using 10% HCl. Hydrolysis conditions are preferably atmospheric pressure and 20.degree.-50.degree. C with ambient temperature the most preferable being most convenient and economical.
The 2-mercapto-1,4-diones produced according to the process of our invention are useful for altering, modifying, or enhancing the organoleptic properties of consumable materials, more particularly, foodstuffs. Thus, for example, 3-mercapto-2,5-hexanedione has a roasted meat aroma and a roasted meat flavor at concentrations of 2 ppm with a threshhold value at 0.5 ppm. 3-Mercapto-2,5-hexanedione evaluated at 12.5 ppm adds a slight sulfury note (which indeed is desirable) to beef bouillon. 3-Mercapto-2,5-hexanedione adds chicken sulfury notes to chicken broth at 2.5 ppm.
The 3-mercapto-1,4 dione derivatives and mixtures thereof produced according to the present invention can be used to alter, vary, fortify, modify, enhance, or otherwise improve the organoleptic properties, including flavor and/or aroma of a wide variety of materials which are ingested, consumed, or otherwise organoleptically sensed.
The term alter in its various forms will be understood herein to mean the supplying or imparting a flavor character or note to an otherwise bland, relatively tasteless substance, or augmenting an existing flavor characteristic where the natural flavor is deficient in some regard, or supplementing the existing flavor or aroma impression to modify the organoleptic character. The materials which are so altered are generally referred to herein as consumable materials.
The term enhance is used herein to mean the intensification of a flavor or aroma characteristic or note without the modification of the quality thereof. Thus enhancement of a flavor or aroma means that the enhancement agent does not add any additional flavor note.
Such 3-mercapto-1,4-dione derivatives are accordingly useful in flavoring compositions. Flavoring compositions are herein taken to mean those which contribute a part of the overall flavor impression by supplementing or fortifying a natural or artificial flavor in a material, as well as those which supply substantially all the flavor and/or aroma character to a consumable article.
The term foodstuff as used herein includes both solid and liquid ingestible materials for man or animals, which materials usually do, but need not, have nutritional value. Thus, foodstuffs includes meats, gravies, soups, convenience foods, malt and other alcoholic or non-alcoholic beverages, milk and dairy products, nut butters such as peanut butter and other spreads, seafoods, including fish, crustaceans, mollusks, and the like, candies, breakfast foods, baked goods, vegetables, cereals, soft drinks, snack foods, dog and cat foods, other veterinary products, and the like.
When the 3-mercapto-1,4dione derivatives produced according to the process of this invention are used in a food flavoring composition, they can be combined with conventional flavoring materials or adjuvants. Such co-ingredients or flavoring adjuvants are well known in the art for such use and have been extensively described in the literature. Apart from the requirement that any such adjuvant material be ingestibly acceptable, and thus non-toxic or otherwise non-deleterious, conventional materials can be used and broadly include other flavor materials, vehicles, stabilizers, thickeners, surface active agents, conditioners, and flavor intensifiers.
Examples of preferred co-flavoring adjuvants are:
Methyl thiazole alcohol (4-methyl-5-betahydroxyethyl thiazole);
2-Methyl butanethiol;
4-Mercapto-2-butanone;
3-Mercapto-4-pentanone;
1-Mercapto-2-propanone;
Benzaldehyde;
Furfural;
Furfural alcohol;
2-Mercapto propionic acid;
2-Pentene;
Alkyl pyrazine;
Methyl pyrazine;
2-Ethyl-3-methyl pyrazine;
Tetramethyl pyrazine;
Polysulfides;
Dipropyl disulfides;
Methyl benzyl disulfides;
Alkyl thiophenes;
2-Butyl thiophene;
2,3-Dimethyl thiophene;
5-Methyl furfural;
Acetyl furan;
2,4-Decadienal;
Guiacol;
Phenyl acetaldehyde;
.delta.-Decalactone;
d-Limonene;
Acetoin;
Amyl acetate;
Maltol;
Ethyl butyrate;
Levulinic acid;
Piperonal;
Ethyl acetate;
n-Octanal;
n-Pentanal;
Hexanal;
Diacetyl;
Monosodium glutamate;
Sulfur-containing amino acids;
Cysteine;
Hydrolyzed vegetable protein;
Hydrolyzed fish protein; and
Tetramethyl pyrazine
The 3-mercapto-1,4 dione derivatives, or the compositions incorporating them, as mentioned above, can be combined with one or more vehicles, or carriers for adding them to the particular product. Vehicles can be edible or otherwise suitable materials such as ethyl alcohol, propylene glycol, water, and the like. Carriers include materials such as gum arabic, carrageenan, other gums, and the like. The 3-mercapto-1,4 dione compounds according to this invention can be incorporated with the carriers by conventional means such as spray-drying, drum-drying, and the like. Such carriers can also include materials for coacervating the 3-mercapto-1,4 dione derivatives (and other flavoring ingredients, as present) to provide encapsulated products. When the carrier is an emulsion, the flavoring composition can also contain emulsifiers such as mono- and diglycerides of fatty acids and the like. With these carriers or vehicles, the desired physical form of the composition can be prepared.
The quantity of 3-mercapto-1,4 dione derivatives or mixtures thereof utilized should be sufficient to impart the desired flavor characteristic to the product, but on the other hand, the use of an excessive amount of the derivative is not only wasteful and uneconomical, but in some instances too large a quantity may unbalance the flavor or other organoleptic properties of the product consumed. The quantity used will vary depending upon the ultimate foodstuff; the amount and type of flavor initially present in the foodstuff; the further process or treatment steps to which the foodstuff will be subjected; regional and other preference factors; the type of storage, if any, to which the product will be subjected, and the preconsumption treatment, such as baking, frying, and so on, given to the product by the ultimate consumer. Accordingly, the terminology effective amount and sufficient amount is understood in the context of the present invention to be quantitatively adequate to alter the flavor of the foodstuff.
It is accordingly preferred that the ultimate compositions contain from about 0.02 parts per million (ppm) to about 250 ppm of 3-mercapto-1,4 dione derivative or derivatives. More particularly, in food compositions it is desirable to use from 0.05 ppm to 100 ppm for enhancing flavors and in certain preferred embodiments of the invention, from about 0.2 to 50 ppm of the derivatives are included to add positive flavors to the finished product. All parts, proportions, percentages, and ratios herein are by weight unless otherwise indicated.
The amount of 3-mercapto-1,4 dione material or materials of our invention to be utilized in flavoring compositions can be varied over a wide range depending upon the particular quality to be added to the foodstuff. Thus, amounts of one or more derivatives according to the present invention of from about 2 ppm up to 80 or 90 percent of the total flavoring composition can be incorporated in such compositions. It is generally found to be desirable to include from about 10 ppm up to about 0.1 percent of the 3-mercapto-1,4 dione derivatives in such compositions.
The following examples I, II, III, IV, V and VII are given to illustrate embodiments of the invention as it is preferably preferred to practice it. Example VI is given to illustrate the usefulness of the products produced by the process of our invention. It will be understood that these examples are illustrative and the invention is not to be considered as restricted thereto except as indicated in the appended claims.

EXAMPLE I
PREPARATION OF CIS-3-HEXENE-2,5-DIONE
In a 1000 ml round bottom flask fitted with condenser and magnetic stirrer are placed 200 g of 2,5-dimethoxy-2,5-dimethyl-2,5-dihydrofuran and 200 ml of a 1% aqueous acetic acid solution. The resulting solution is heated to reflux, refluxed for 2 minutes, cooled with an ice bath to 25.degree. C and 625 ml of a 2% sodium bicarbonate solution is added. The solution is saturated by addition of 23 g of sodium chloride and extracted with methylene chloride (1 .times. 200 ml and 3 .times. 100 ml). After drying over sodium sulfate removal of the methylene chloride in vacuo gives 142 g of crude cis-3-hexene-2,5-dione which by GLC analysis is about 90% product having the structure: ##STR18##
EXAMPLE II
PREPARATION OF 3-THIOACETYL-2,5-HEXANEDIONE
In a 1000 ml round bottom flask fitted with magnetic stirrer, thermometer, addition funnel and reflux condenser are placed 142 g of crude cis-3-hexene-2,5-dione (ex Example I), 380 ml of ether and 5 drops of piperidine. Thio acetic acid (96.6 g) is added over a period of one hour. When about 1/8 of the thio acetic acid is added, the solution begins to reflux which continues during the remainder of the addition. After addition is complete, the mixture is allowed to stand for 85 minutes. Ether is then removed in vacuo (water asperator) to give 235 g of crude material containing about 91% 3-thioacetyl-2,5-hexanedione. Distillation of a 134 g portion of the crude gives 84.5 g of 3-thioacetyl-2,5-hexanedione boiling at 86.degree. to 87.degree. C at 0.5 torr. NMR, IR and mass spectral analyses confirm the structure: ##STR19##
EXAMPLE III
PREPARATION OF 3-MERCAPTO-2,5-HEXANEDIONE
To 150 ml of a 2% sodium hydroxide solution in a flask fitted for stirring is added 10 g of 3-thioacetyl-2,5-hexanedione. After stirring for one hour the pH of the mixture is adjusted to 5-6 by the addition of dilute (10%) hydrochloric acid, the solution is saturated with sodium chloride solution and extracted with ether (4 .times. 25 ml). The ether extracts are combined, washed with saturated sodium chloride solution (15 ml), dried and concentrated in vacuo to give 6.2 g of crude 3-mercapto-2,5-hexanedione. Vacuum distillation gives 2.5 of 3-mercapto-2,5-hexanedione boiling at 57.degree.-59.degree. C at 0.85 torr. NMR, IR and mass spectral analyses confirm the structure as 3-mercapto-2,5-hexanedione.
EXAMPLE IV
PREPARATION OF 2-MERCAPTO-1,4-BUTANE-DIAL
A. Preparation of 2-Butene-1,4-Dial
A mixture of 2,5-dimethoxy-2,5-dihydrofuran (20 g), water (80 ml) and acetic acid (3 drops) is stirred for 105 minutes at room temperature, 22 minutes at 40.degree. C and 90 minutes between 60.degree. C and 75.degree. C. GLC analysis at this point indicates 15.7% starting material and 83.5% 2-butene-1,4-dial. The mixture is cooled to 25.degree. C and sodium bicarbonate (0.3 g) is added.
B. Preparation of 3-Thioacetyl-1,4-Butanedial
To the aqueous solution obtained in Section A supra, is added 10 g of thio acetic acid during a 14 minute period. During the addition, the temperature is kept below 30.degree. C by intermittent application of a cooling bath. After 110 minutes, the reaction mixture is extracted with methylene chloride (3 .times. 35 ml). The combined methylene chloride extracts are dried and then concentrated in vacuo to give 17.8 g of yellow oil containing about 80% 2-thioacetyl-1,4-butanedial. The compound is identified through mass spectral, NMR and IR analyses as having the structure: ##STR20##
M.S. - No molecular ion; remaining peaks in decreasing intensity - 43, 29, 27, 45, 55, 60, 84, 100 and 142 m/e units. NMR (CDCl.sub.3) 2.38 (s,3) 3.02 (multiplet 2,J=1OH.sub.z), 4.46 (r,lJ=1OHz) 9.40 (s,l) and 9.68 (s,l) ppm. IR (thin film) - 2850, 2750, 1720, 1700 (shoulder), 1388, 1352, 1132 and 958 cm.sup.-.sup.1.
C. Preparation of 3-Mercapto-1,4-Butanedial
To 150 ml of a 2% sodium hydroxide solution in a flask fitted for stirring is added 10 g of 3-thioacetyl-1,4-butanedial prepared according to part B supra. After stirring for one hour the pH of the mixture is adjusted to 5-6 by the addition of dilute (10%) hydrochloric acid, the solution is saturated with sodium chloride solution and extracted with ether (4 .times. 25 ml). The ether extracts are combined, washed with saturated sodium chloride solution (15 ml), dried and concentrated in vacuo to give 6.2 g of crude 3-mercapto-1,4-butanedial. Vacuum distillation gives 2.5 g of 2-mercapto-1,4 butanedial. NMR, IR and mass spectral analyses confirm the structure as 2-mercapto-1,4-butanedial.
EXAMPLE V
PREPARATION OF 3-MERCAPTO-4-OXO-PENTANAL
A. 4-Oxo-2-Pentenal
Into a 5 liter, three-necked flask fitted with mechanical stirrer, thermometer and vacuum take-off are placed 600 g of 2-methyl-2,5-dimethoxy-2,5-dihydrofuran and 2400 ml of deionized water. After 20 minutes of stirring at room temperature, the mixture becomes homogeneous and has a pale yellow green color. Analysis of a sample of the reaction mixture by GLC after 3.25 hours shows 22% methanol, 67% 4-oxo-2-pentenal and 9% starting material. Vacuum (26 torr) is applied to the reaction mixture while maintaining the temperature of the reaction mixture between 25.degree. and 30.degree. C. After 3.25 hours GLC analysis shows 13% methanol, 82% 4-oxo-2-pentenal and 3.2% starting material. The vacuum is removed and the reaction mixture is allowed to stand at room temperature overnight. Analysis after standing overnight shows 12.9% methanol, 85% 4-oxo-2-pentenal and 2.1% starting material.
B. 3-THIOACETYL-4-OXO-PENTANAL
In a 5 liter, three-necked flask fitted with mechanical stirrer, thermometer and addition funnel are placed 2325 ml of the solution obtained in (A) and 2 ml of piperidine diluted in 5 ml of water. To this solution is added a mixture of thio acetic acid (292.3 g) and piperidine (13 ml) over a 20 minute period. After standing an additional 10 minutes, 20 ml of concentrated hydrochloric acid is added, the resulting mixture poured into a separatory funnel and the oil layer removed. The aqueous layer is extracted with benzene (500 ml) and methylene chloride (2 .times. 500 ml). The benzene extract is combined with the oil layer and the mixture is dried over sodium sulfate. The methylene chloride extracts are combined and dried over sodium sulfate. Solvent removal in vacuo (40.degree.-45.degree. C both at 15 torr) gives 414.5 g of crude oil from the benzene extract and 172.5 g of crude oil from the methylene chloride extracts. The crude oil is distilled under vacuum to give 3-thioacetyl-4-oxo-pentanal boiling at 94.degree.-98.degree. C at 0.3-0.55 mm Hg.
C. 3-Mercapto-4-Oxo-Pentanal
To 150 ml of a 2% sodium hydroxide solution in a flask fitted for stirring is added 10 g of 3thioacetyl-4-oxo-pentanal prepared according to the procedure of part B supra. After stirring for one hour the pH of the mixture is adjusted to 5-6 by the addition of dilute (10%) hydrochloric acid, the solution is saturated with sodium chloride solution and extracted with ether (4 .times. 25 ml). The ether extracts are combined, washed with saturated sodium chloride solution (15 ml), dried and concentrated in vacuo to give 6.2 g of crude 3-mercapto-4-oxo-pentanal. Vacuum distillation gives 2.5 g of 3-mercapto-4-oxo-pentanal. NMR, IR and mass spectral analyses confirm the structure as 3-mercapto-4-oxo-pentanal.
EXAMPLE VI
The following formulation is prepared:
______________________________________Ingredient Parts by Weight______________________________________Liquid hydrolyzed vegetable protein 90.004-Methyl-5-beta-hydroxy-ethyl thiazole 5.00Tetrahydro thiophene-3-one 1.00Furfuryl mercaptan 0.012-nonenal 0.50Difurfuryl disulfide 0.49Dimethyl sulfide 0.50Methyl mercaptan 0.503-mercapto-2,5-hexanedione 2.00______________________________________
The 3-mercapto-2,5-hexanedione imparts a roasted meat taste to the above formula and ties in and rounds up the other meat-like chemicals in the formula.
EXAMPLE VII
PREPARATION OF 3-MERCAPTO-4-OXO-HEPTANAL
A. Preparation of 2-Propyl-2,5-Dimethoxy-2,5-Dihydro Furan From 2-Propyl Furan ##STR21##
Into a 500 ml three-necked reaction flask equipped with mechanical stirrer, calcium carbonate drying tube and thermometer, the following materials are placed:
______________________________________(i) 2-Propyl furan 25.0 g (0.227 moles)(ii) Methanol, absolute 180 ml(iii) Sodium carbonate 47.1 g (0.454 moles)______________________________________
The reaction mass is cooled to -10.degree. C using a dry-ice acetone bath. Over a period of 20 minutes, a solution of 36.3 grams of bromine in 70 ml absolute methanol is added dropwise while maintaining the reaction mass at -12.degree. C to -13.degree. C. After the addition of the bromine solution, the reaction mass is stirred for 1.5 hours while maintaining same at -10.degree. C.
The reaction mass is then mixed with 450 ml of saturated sodium chloride solution. The resulting mixture is suction filtered and the filter cake is washed with 100 ml of methylene dichloride. The resultant filtrate and washings are placed in a separatory funnel and the lower organic phase is drawn off. The aqueous phase is extracted with two 100 ml portions of methylene dichloride and the organic solutions are combined. The organic solution is then dried over anhydrous sodium sulfate and filtered; and then concentrated in vacuo to a yellow liquid weighing 32.7 grams. The major peak of this material determined by GLC contains 2-propyl-2,5-dimethoxy-2,5-dihydro furan (GLC conditions: F and M 5750; 8 feet .times. 1/4 inch SE-30; programmed from 130.degree.-225.degree. C at 4.degree. C per minute, with an He flow rate of 80 ml/minute, chart speed 0.25 inch per minute).
B. Preparation of 4-Oxo-2-Heptenal
Reaction: ##STR22##
Into a 250 ml three-necked reaction flask equipped with mechanical stirrer and thermometer the following materials are added:
______________________________________(i) 2-Propyl-2,5-dimethoxy 32.7 g 2,5-dihydrofuran prepared (0.16 moles) according to the process of Part A(ii) Water (distilled) 325 ml______________________________________
The reaction mass is stirred for a period of 4 hours at 24.degree. C. At the end of this period of time, the reaction mass exists in two phases; an aqueous upper phase and an organic lower phase. The aqueous upper phase is decanted and placed in a one liter vessel for the following reaction C.
C. Reaction of 4-Oxo-Heptenal with Thioacetic Acid ##STR23##
To the stirred aqueous solution produced in Part B, supra, of 4-oxo-2-heptenal is added 0.4 ml piperidine. After the piperidine addition, 12.4 grams of thioacetic acid is added to the reaction mass over a period of 4 minutes while maintaining the reaction mass at a temperature in the range of 27.degree.-32.degree. C. After the thioacetic acid addition is complete, the reaction mass is stirred for 1.5 hours. The reaction mass is then placed in a separatory funnel and extracted with 100 ml of methylene dichloride. The methylene dichloride solution is then separated, dried over anhydrous sodium sulfate and concentrated to an orange oil weighing 23.8 grams. This orange oil is analyzed using GLC, NMR and IR analyses and determined to be substantially 3-thioacetyl-4-oxo-heptanal.
Mass Spectral Analysis Molecular Ion, then in decreasing intensity: 202, 43, 28, 71, 55, 41, 97, 83 m/e
D. Preparation of 3-Mercapto-4-Oxoheptanal
To 150 ml of a 2% sodium hydroxide solution in a flask fitted for stirring is added 10 g of 3-thioacetyl-4-oxoheptanal-1 prepared according to the procudure of part C, supra. After stirring for one hour the pH of the mixture is adjusted to 5-6 by the addition of dilute (10%) hydrochloric acid, the solution is saturated with sodium chloride solution and extracted with ether (4 .times. 25 ml). The ether extracts are combined, washed with saturated sodium chloride solution (15 ml), dried and concentrated in vacuo to give 6.2 g of crude 3-mercapto-4-oxo-heptanal-1. Vacuum distillation gives 2.5 g of 3-mercapto-4-oxo-heptanal-1. NMR, IR and mass spectral analysis confirm the structure as 3-mercapto-4-oxoheptanal-1.

Number	Name	Date
2630452	Crouch et al.	Mar 1953
3441589	Oswald	Apr 1969
3836563	Evers et al.	Sep 1974

	Number	Date	Country
Parent	478354	Jun 1974
Parent	386452	Aug 1973

Process for producing 2-mercapto-1,4-diones

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Reid, Chemistry of Bivalent Sulfur, pp. 15-16.
Walton et al., J.A.C.S., vol. 77, pp. 5144-5147 (1955).