the invention relates to compounds of the formula ## str4 ## wherein r 1 and r 2 , independently , are hydrogen , halogen , methyl , methoxy or p - chlorophenoxy ; y is cyano or a group of the formula ## str5 ## wherein r 3 is hydroxy , lower alkoxy , hydroxy -( lower alkoxy ) or a group of the formula -- n ( r 4 )( r 5 ), wherein r 4 is hydrogen and r 5 is cycloalkyl containing from 3 to 6 carbon atoms , or r 4 and r 5 , independently , are hydrogen or lower alkyl , or r 4 and r 5 , when taken together with the nitrogen atom to which they are attached , are a 5 - or 6 - membered heterocyclic ring ; a is methylene , ethylene , propylene or -- och 2 ch 2 --; and n is an integer from 2 to 10 inclusive , or , as used herein , the term &# 34 ; lower alkyl &# 34 ; denotes a straight or branched chain saturated hydrocarbon containing 1 to 7 carbon atoms , for example , methyl , ethyl , propyl , isopropyl , butyl , t - butyl , neopentyl , pentyl , heptyl or the like . the term &# 34 ; lower alkoxy &# 34 ; denotes an alkyloxy in which the alkyl group is as described above , for example , methoxy , ethoxy , propoxy , pentoxy , or the like . the term &# 34 ; halogen &# 34 ; denotes all the halogens , i . e ., bromine , chlorine , fluorine or iodine . exemplary of the group -- n ( r 4 )( r 5 ) are amino , monomethylamino , dimethylamino , monoethylamino , diethylamino , monocyclopropylamino , monocyclobutylamino , monocyclopentylamino , monocyclohexylamino , pyrrolidino , piperidino or morpholino . a preferred group of compounds of formula i comprises those wherein r 1 is hydrogen , namely , those compounds which are unsubstituted or monosubstituted in the phenyl ring . other preferred compounds of formula i are those wherein r 2 is halogen , preferably chlorine , and y is ## str6 ## preferably lower alkoxycarbonyl or carboxy , as well as those wherein a is methylene and n is 2 , 3 or 4 , preferably 3 . a more preferred compound of formula i is 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester . the compounds of formula i wherein y is -- cooh form salts with pharmaceutically acceptable bases . exemplary of the salts of the acids of formula i are ammonium salts , alkali metal salts , such as the sodium or potassium salts , alkaline earth metal salts , such as calcium salts , and salts with amines , such as monoalkylamines , dialkylamines or trialkylamines . according to the process of the present invention , the thiocarbamoylthio fatty acid derivatives , i . e ., the compounds of formula i of the invention , and salts of such compounds , wherein y is carboxy , with bases , can be prepared by reacting a compound of the formula ## str7 ## wherein r 1 , r 2 and a are as previously described and m + is na + , k + or nh 4 + , wherein x is halogen and y and n are as previously described , or with an alkali metal salt of a halocarboxylic acid of the formula or reacting an isothiocyanate of the formula ## str8 ## wherein r 1 , r 2 and a are as previously described , with a mercaptan of the formula wherein y and n are as previously described , and , if desired , saponifying an ester so obtained or an amide so obtained to an acid , reesterifying an ester obtained , esterifying an acid so obtained or converting same into a salt with a base , hydrolyzing a nitrile so obtained to an amide or dehydrating an amide so obtained to a nitrile . the reaction of a compound of formula ii with a compound of formula iii is conveniently carried out in an inert solvent , such as water , acetone , an alcohol , dimethylformamide , dioxane or dioxane / water . the reaction can be carried out at room temperature , although in certain cases it may be converient to warm the reaction mixture . the reaction of an isothiocyanate of formula v with a mercaptan of formula vi is conveniently carried out in an inert solvent , for example , toluene , or an ether , such as dioxane , at a temperature in the range of from about - 20 ° c . to the reflux temperature of the reaction mixture , preferably at about 0 ° c . the optional subsequent transformations at the group y can be carried out in accordance with methods known per se . the saponification of an ester or amide of formula i to an acid of formula i can be carried out , for example , with dilute acids , such as half - concentrated hydrochloric acid , conveniently while warming . the esterification of an acid of formula i can be carried out by reacting a suspension or solution of said acid with an excess of alcohol and thionyl chloride at a temperature in the range of from about 0 ° c . to about room temperature . the preparation of a salt of an acid of formula i can be carried out by reacting the acid with the stoichiometric amount of a base , such as an alkali metal hydroxide , ammonium hydroxide , an alkaline earth metal hydroxide , ammonium hydroxide , an alkaline earth metal hydroxide or an amine . a nitrile of formula i can be hydrolyzed to a corresponding amide of formula i using an acid such as hydrochloric acid or sulfuric acid . an amide of formula i can be dehydrated to a corresponding nitrile of formula i using phosphorus oxychloride or thionyl chloride and dimethylformamide . the compounds of formula ii can be prepared by reacting a compound of the formula ## str9 ## wherein r 1 , r 2 and a are as previously described , with sodium hydroxide , potassium hydroxide or ammonium hydroxide and carbon disulfide . this reaction is preferably carried out in a water - miscible inert solvent such as acetonitrile at a low temperature , for example , in the range of from about 0 ° c . to room temperature . the compounds of formulas iii , iv , v , vi and vii are known compounds or can be prepared in an analogous manner to known compounds . the thiocarbamoylthio fatty acid derivatives provided by the invention can be utilized as medicaments , particularly as lipid - lowering agents , due to their activity in lowering the blood fat level . when 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester is repeatedly administered to male rats ( 5 times at a rate of 90 mg / kg p . o .) there was brought about , for example , a 30 - 40 % reduction of triglyceride and a 20 - 30 % reduction of cholesterol in serum taken from the rats . this result is achieved with half of the dosage which would be required using the known lipid - lowering agent clofibrate (&# 34 ; merck index ,&# 34 ; 1968 , page 270 ). for administration to a warm - blooded animal requiring such treatment , there come into consideration dosages of 30 to 60 mg of a thiocarbamoylthio fatty acid derivative of formula i of the invention per kg of body weight . the thiocarbamoylthio fatty acid derivatives of formula i of the invention and the salts thereof with pharmaceutically acceptable bases can be used as medicaments . for example , they can be used in the form of pharmaceutical preparations which contain them in association with one or more compatible pharmaceutical carrier materials . such carrier materials can be an inert organic or inorganic carrier material suitable for enteral or parenteral administration , for example , water , gelatin , gum arabic , lactose , starch , magnesium stearate , talc , vegetable oils , polyalkyleneglycols , or the like . the pharmaceutical preparations can be made up in a solid form , for example , as tablets , dragees or capsules , or in a liquid form , for example , as solutions , suspensions or emulsions . the pharmaceutical preparations may be sterilized and / or may contain adjuvants , such as preserving , stabilizing , wetting or emulsifying agents , salts for varying osmotic pressure or buffers . the pharmaceutical preparations may also contain therapeutically valuable substances other than the thiocarbamoylthio fatty acid derivatives provided by this invention . the examples which follow further illustrate the invention . all temperatures are in degrees centigrade , unless otherwise mentioned . to a solution of 160 g . of 4 - bromobutyric acid ethyl ester in 1125 ml . of absolute dimethylformamide were added gradually under an atmosphere of argon at 0 ° c . while stirring well and cooling , 172 . 3 g . of ammonium ( n - 4 - chlorobenzyl ) dithiocarbamate , the temperature was maintained constant . the slightly yellow solution was stirred overnight at room temperature , diluted with 1500 ml . of water and extracted four times with 500 ml . of ethyl acetate each time . the combined organic phases were washed three times with 200 ml of saturated sodium chloride solution each time and dried over 80 g . of magnesium sulfate with the addition of carbon , filtered and evaporated under reduced pressure . the resulting crystalline residue was recrystallized from 700 ml . of diisopropyl ether , and 218 g . of 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 61 °- 62 ° c . was obtained . the dithiocarbamate utilized as the starting material can be prepared as follows : 260 ml . of concentrated ammonia solution were treated under an atmosphere of argon , and while cooling by means of ice / methanol bath at ≦- 10 ° c . within about 20 minutes , with 164 . 5 g . of carbon disulfide and the mixture was subsequently stirred for an additional 15 minutes at the same temperature . 245 g . of 4 - chlorobenzylamine dissolved in 122 ml . of acetonitrile were then slowly added , the temperature still maintained at ≦- 10 ° c . subsequently , the mixture was stirred overnight at room temperature and then cooled in an ice - bath to 0 ° c . the precipitated crystals were removed by filtration under suction , washed successively with acetonitrile and diethyl ether and dried to a constant weight under reduced pressure at 70 °- 80 ° c ., and 390 g . of ammonium ( n - 4 - chlorobenzyl ) dithiocarbamate having a melting point of 140 °- 142 ° c . was obtained . in an analogous manner to that described above , the following thiocarbamoylthio fatty acid derivatives were prepared : 4 -[( benzylthiocarbamoyl ) thio ]- butyric acid ethyl ester having a melting point of 56 °- 57 ° c . ; 3 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- propionic acid ethyl ester having a melting point of 67 °- 68 ° c . ; 11 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- undecanoic acid ethyl ester having a melting point of 51 . 5 °- 52 . 5 ° c . ; 5 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- valeric acid ethyl ester having a boiling point of 135 °- 137 ° c ./ 0 . 08 torr ; 4 -{[( 2 , 5 - dichlorobenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 62 °- 63 ° c . ; 4 -{[( p - methoxybenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 47 °- 48 ° c . ; 4 -{[( p - methylbenzyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 61 °- 62 ° c . ; 4 -{[[ 2 -( p - chlorophenoxyphenoxy ) ethyl ] thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 72 °- 74 ° c . ; and 4 -{[[ 2 -( p - chlorophenoxy )- ethyl ] thiocarbamoyl ] thio }- butyric acid ethyl ester having a melting point of 63 °- 64 ° c . 20 . 3 g . of ammonium 3 -[( p - chlorophenyl ) propyl ] dithiocarbamate were added slowly while cooling with ice to a solution of 12 . 4 ml . of 4 - bromobutyric acid ethyl ester in 120 ml . of ethanol and the mixture was stirred overnight at room temperature . after evaporation in vacuo , the residue was partitioned between water and ethyl acetate , the aqueous phase extracted three times with ethyl acetate , the combined organic phases washed with saturated sodium chloride solution , dried over magnesium sulfate and again concentrated in vacuo . the remaining oily residue was chromatographed on silica gel using toluene / ethyl acetate for the elution , and 19 . 0 g . of 4 -{[[ 3 -( p - chlorophenyl )- propyl ] thiocarbamoyl ] thio }- butyric acid ethyl ester , as a colorless viscous oil , were obtained . 4 -{[( p - chlorophenethyl ) thiocarbamoyl ] thio }- butyric acid ethyl ester was prepared in the form of an oil in an analogous manner to that described in the preceding paragraph . 10 g . of 4 -{[[ 3 -( p - chlorophenyl ) propyl ] thiocarbamoyl ]- thio }- butyric acid ethyl ester dissolved in 100 ml . of acetic acid were stirred under slight reflux for 8 hours with 50 ml . of half - concentrated hydrochloric acid . the mixture was evaporated in vacuo , the residue recrystallized from carbon tetrachloride , and 4 . 4 g . of 4 -{[[( p - chlorophenyl ) propyl ]- thiocarbamoyl ] thio }- butyric acid having a melting point of 98 °- 100 ° c . were obtained . the following thiocarbamoylthio fatty acid derivatives were prepared in a corresponding manner : to 37 . 5 g . of 4 - bromobutyronitrile in 350 ml . of absolute dimethylformamide were added , while cooling with ice , 53 . 7 g . of ammonium ( n - 4 - chlorobenzyl ) dithiocarbamate and the mixture was stirred overnight at room temperature . after evaporation in vacuo , the product was taken up in ethyl acetate , washed with water , dried , concentrated and the residue crystallized from diethyl ether / diisopropyl ether , whereby 48 . 2 g . of 3 - cyanopropyl ( p - chlorobenzyl ) dithiocarbamate having a melting point of 61 °- 63 ° c . were obtained . 29 . 2 g . of 3 - cyanopropyl ( p - chlorobenzyl ) dithiocarbamate were suspended in 150 ml . of concentrated hydrochloric acid and stirred at room temperature for 2 hours . the mixture was diluted with water and extracted with ethyl acetate . after washing , drying and concentration of the ethyl acetate phases , 18 . 1 g . of 3 - carbamoylpropyl ) p - chlorobenzyl ) dithiocarbamate were crystallized from ethyl acetate / diisopropyl ether ; melting point 123 °- 125 ° c . 15 . 8 g . of γ - chloro - n - methylbutyric acid amide dissolved in 200 ml . of absolute ethanol were treated with 24 . 8 g . of ammonium ( n - 4 - chlorobenzyl ) dithiocarbamate . after a clear solution had formed , it was stirred at 60 ° c . for 1 . 5 hours . thereafter , it was concentrated in vacuo , and the residue taken up in water and extracted with ethyl acetate . the organic phases were washed with saturated sodium chloride solution , dried over magnesium sulfate and concentrated . the residue was crystallized from ethyl acetate / diisopropyl ether , and 12 . 7 g . of 3 -( methylcarbamoyl )- propyl ( p - chlorobenzyl )- dithiocarbamate , having a melting point of 139 °- 141 ° c . were obtained . the following thiocarbamoylthio fatty acid derivatives were prepared in an analogous manner : 1 . 5 g . of 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid were dissolved in 30 ml . of diethyl ether and treated with an excess of an ethereal diazomethane solution . the resulting solution was evaporated . the residue was recrystallized from cyclohexane , and 1 . 2 g . of 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid methyl ester having a melting point of 60 °- 62 ° c . were obtained . 9 . 15 g . of 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid dissolved in 120 ml . of ethyleneglycol were treated dropwise at - 5 ° c . with 8 . 7 ml . of thionyl chloride and the mixture was subsequently stirred at room temperature for 3 hours . then , the solution was made alkaline with 2 - n sodium hydroxide solution and extracted with chloroform . the chloroform phases were washed with saturated sodium chloride solution , dried over magnesium sulfate and concentrated . recrystallization of the residue from diisopropyl ether gave 8 . 1 g . of 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid 2 - hydroxyethyl ester having a melting point of 77 °- 78 ° c . the following thiocarbamoylthio fatty acid derivatives were prepared in an analogous manner : 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid isopropyl ester having a melting point of 76 °- 77 ° c . ; 4 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- butyric acid butyl ester having a melting point of 66 °- 67 ° c . ; and 4 -{[( p - chlorophenethyl ) thiocarbamoyl ] thio }- butyric acid 2 - hydroxyethyl ester having a melting point of 69 °- 70 ° c . to a solution of 1 . 06 g . of 3 - mercaptopropionic acid in 5 ml . of toluene and 2 . 0 g . of triethylamine , there was added with cooling 1 . 83 g . of p - chlorobenzylisothiocyanate . two phases formed . the mixture was acidified with 1 - n hydrochloric acid and extracted with chloroform . the chloroform phases were washed with water , dried over magnesium sulfate and concentrated . the residue was recrystallized from acetonitrile , and 2 . 1 g . of 3 -{[( p - chlorobenzyl ) thiocarbamoyl ] thio }- propionic acid having a melting point of 126 °- 127 ° c . were obtained . 3 -{[( p - chlorophenethyl ) thiocarbamoyl ] thio }- propionic acid having a melting point of 104 . 5 °- 105 ° c . was prepared in an analogous manner . the following example illustrates a pharmaceutical preparation containing the thiocarbamoylthio fatty acid derivatives provided by the invention : tablets containing the following ingredients were produced in a manner known per se : ______________________________________ingredient per tablet______________________________________4 -{[( p - chlorobenzyl ) thiocarbamoyl ]- thio }- butyric acid ethyl ester 50 . 00 mg . polyethyleneglycol 200 . 00 mg . lactose 70 . 00 mg . microcrystalline cellulose 70 . 00 mg . polyvinylpyrrolidone 100 . 00 mg . magnesium stearate 10 . 00 mg . total weight 500 . 00 mg . ______________________________________