the flavour precursors of the present invention are derived from a furenidone and a carbonyl compound , both of which possess valuable flavouring properties . the nature of the carbonyl compound determines whether the precursor reverts under mild or under more severe conditions to the flavouring furenidone . under acid or neutral reaction conditions the following addition reaction of the furenidone takes place : ## equ1 ## in this general formula r 1 and r 2 represent a lower c 1 - c 4 alkyl group , preferably methyl or ethyl , while r 3 represents hydrogen or a methyl group and r 4 represents hydrogen or an organic radical consisting of 1 - 14 carbon atoms , hydrogen and 0 - 2 oxygen atoms , preferably a hydrocarbyl , more in particular an alkyl group or alkenyl group containing 2 - 10 carbon atoms . furthermore , in case r 3 represents a methyl group , r 4 should not contain more than 4 carbon atoms . these novel carbonyl addition compounds occur in two stereoisomeric forms in case r 3 and r 4 represent different groups and both forms are suitable flavour precursors for the purpose of this invention . particularly preferred carbonyl compounds which can be added to the furenidone are aliphatic saturated and unsaturated aldehydes and methyl - ketones such as acetaldehyde propanal , octanal , acetone , methylethylketone , cis - 3 - hexenal and cis - 4 - heptenal . aromatic and heterocyclic aldehydes such as phenylacetaldehyde , benzaldehyde , furfuraldehyde , methylfurfuraldehyde and hydroxymethylfurfuraldehyde , can also be used . carbonyl compounds containing 6 - 8 carbon atoms are preferred . the addition reaction takes place smoothly in a suitable polar solvent such as water in the presence of an acid - base catalyst under neutral or acid conditions at room temperature although higher - up to 100 ° c - and lower temperatures , above 5 ° c , can also be used . atmospheric pressures are suitably employed . however , too high temperatures favour reversion . the novel addition compounds of the alkyl substituted furenidones can be isolated without undue difficulties and may be used according to the present invention for incorporation into foodstuffs , in particular in foodstuffs which are heated to temperatures over 100 ° c when being prepared for consumption . such foodstuffs are e . g . shortenings , fats , margarines , especially bakery frying margarines , dried sterilised or deepfrozen soups , meat products , meatballs , ready - made meals , meat imitating products such as those known as texturised vegetable protein , mesophase , and various products used in bakeries , e . g . reinforced flour , baking aids etc . the amount of addition compound incorporated into the foodstuff ranges from 0 . 1 - 500 parts per million , dependent on the particular precursor and foodstuff , preferably 1 - 100 ppm . incorporation into the product may take place by adding the addition compound to the ingredients , spraying over the formed products etc . the addition compounds are usually used in conjunction with further flavouring agents or precursors thereof , such as e . g . amino acids , nucleotides , carboxylic acids , sweetening substances , etc . of course the actual combination is determined by the type of product . by way of illustration the following examples are given to elucidate the invention : in a round - bottomed flask equipped with a stirrer and a condensor , 12 . 8 g ( 0 . 1 mole ) of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone and 44 g ( 1 . 0 mole ) of acetaldehyde were introduced into a solution of 3 . 0 g of oxalic acid in 100 ml of water . the mixture was stirred and refluxed for 1 hour . after cooling , the mixture was extracted 5 times with 25 ml portions of chloroform and the organic solvent was evaporated off . the residue was purified by chromatography on 50 g of polyamide . after elution by means of a 50 / 50 mixture of ether and petroleum ether , 9 . 4 g of the title compound was obtained ( which corresponds to a yield of 54 %). recrystallization from ether gave the pure product with m . p . 112 - 114 ° c ). infrared absorptions ( in kbr disc .) were at 3400 , 3200 , 1697 , 1610 , 1450 , 1370 , 1250 , 1072 , 1066 , 1005 and 924 cm . sup . - 1 . the nmr spectrum [ in cdcl 3 , internal standard si ( ch 3 ) 4 ] had signals at δ = 1 . 17 ( doublet ), δ = 1 . 41 ( singlet ), δ = 2 . 27 ( singlet ), δ = 3 . 81 ( quartet ), 4 . 3 - 5 . 7 ( broad peak ). the mass spectrum showed peaks at m / e 172 , 157 , 155 , 154 , 128 , 101 , 85 , 83 , 72 , 45 , 43 . 50 mg of the compound thus obtained was heated in 0 . 5 ml of water to a temperature of 100 ° c . the breakdown of the compound into 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone and acetaldehyde was followed by investigating the n . m . r . signals at intervals . in particular the diminishing signal of the starting compound at 0 . 99 ppm ( with respect to dimethylsulfoxide ) and the increasing signals of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone at 1 . 25 and 2 . 08 ppm were followed . the other signals present in the spectrum recorded in cdcl 3 solution are obscured by the water signal . from the change in signals it was deduced that after about 48 hours 50 % of the starting material had been converted into the 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone . in an aprotic solvent 50 % was converted within a fraction of an hour to 24 hours , as a similar experiment showed , whereas at 160 ° c 50 % was converted in 1 / 4 hour . a mixture of 5 g of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone and 10 . 6 g of benzaldehyde was added to a mixture of 20 ml of water , 20 ml of dioxan and 0 . 5 g of oxalic acid . the mixture was then refluxed for 4 hours , cooled and extracted with chloroform . the chloroform extract was evaporated and the residue purified by column chromatography over polyamide using ether - light petroleum 50 / 50 as the eluent ; 2 . 7 g ( 30 % yield ) of the title compound was obtained which was recrystallized from chloroform , m . p . = 122 °- 124 ° c . infrared absorptions ( kbr disc .) were at 3400 , 1715 , 1635 , 1455 , 1370 , 1240 , 1096 , 1080 , 1042 , 1010 , 910 and 705 cm . sup . - 1 . the nmr spectrum [ solvent cdcl 3 , internal standard si ( ch 3 ) 4 ] had signals at δ = 1 . 22 ( singlet ), δ = 2 . 17 ( singlet ), δ = 4 . 73 ( singlet ), δ = 4 . 9 - 5 . 6 ( broad peak ), δ = 7 . 15 ( singlet ). the mass spectrum showed peaks at m / e 234 , 128 , 107 , 106 , 105 , 85 , 77 , 57 , 55 , 52 , 51 , 50 , 45 , 43 . to a mixture of 6 g ( 0 . 05 mole ) phenylacetaldehyde and 1 . 28 g ( 0 . 01 mole ) of 2 . 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was added 60 mg of boric acid and the mixture was stirred at 80 ° c for 3 hours . after working up the reaction mixture as described earlier , 0 . 57 g ( 23 %) of the title compound was obtained , with melting point 157 . 5 °- 159 ° c . infrared absorptions ( kbr disc .) were at 3500 , 3240 , 1697 , 1616 , 1447 , 1298 , 1240 , 1097 , 1058 , 746 and 703 cm . sup . - 1 . the nmr spectrum [ solvent dmso - d6 + cdcl 3 ( 3 : 2 ), internal standard si ( ch 3 ) 4 ] had signals at δ = 1 . 32 ( singlet ), δ = 2 . 15 ( singlet ), δ = 2 . 35 - 2 . 62 ( multiplet ), δ = 3 . 60 ( multiplet ), δ = 5 . 00 ( doublet ), δ = 7 . 00 ( singlet ), δ = 7 . 98 ( singlet ). the mass spectrum showed peaks at m / e 248 , 230 , 205 , 157 , 128 , 121 , 120 , 111 , 103 , 101 , 91 , 77 , 43 . the addition compound in an aprotic solvent was converted for 50 % to 2 . 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone after heating for 1 / 3 hour at 160 ° c . 0 . 3 g of 2 -( 1 - hydroxyethyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was added to 1000 g of unflavoured margarine and the mixture then heated in a pan for 5 minutes at 160 °- 170 ° c . this flavoured fried margarine was preferred to a fried margarine without addition by 8 out of 11 tasters , who mentioned particularly its sweet , caramel - like aroma . to 100 g of hardened fat 5 mg of 2 -( 1 - hydroxyethyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was added and the mixture was then heated for 5 minutes at 150 ° c . this fat was preferred to a fat without addition by 9 out of 10 tasters who mentioned particularly its mild fruity aroma . a basis for canned beef soup was prepared by adding the following ingredients to 4 liters of water : gramsnoodles 160herb and spices 1 . 6tallow 80vegetables 400monosodium glutamate 16protein hydrolysate 16meat extract 16salt 64raw meat 400 the total amount was divided into two portions of each 2 liters ; 0 . 08 g of 2 -( 1 - hydroxyethyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was added to one of the portions . the second portion , which was used without further addition , served as a comparative example . the mixtures thus obtained were canned in half liter tins and sterilised in an autoclave for 1 hour at 120 ° c . a soup ready for consumption was prepared by adding an equal volume of water to the contents of each tin . after heating the soups were tested and a majority of the flavour evaluation panel preferred the soup with the added flavour precursor because of its more pronounced meaty flavour . grams flour 450 sugar 225 fat 250 water 65 salt 5 baking powder 3 the fat and the sugar were mixed in a hobart mixer ( type : ce 100 ) for 3 minutes at speed 2 . after adding the water , mixing proceeded for another 2 minutes . subsequently the flour , the salt and the baking powder were added , after which the composition was mixed for 10 minutes . the dough was spouted on baking trays in the shape of piped shortcakes and baked for 20 minutes at 180 ° c . in an analogous way piped shortcakes were prepared in which , however , 20 mg of 2 -( 1 - hydroxy - 2 - phenylethyl - 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone were added to the dough . the shortcakes thus prepared were evaluated by a panel in a pair test . the shortcakes to which 2 -( 1 - hydroxy - 2 - phenylethyl - 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone had been added were generally preferred by the members of the panel . a mixture of 10 g of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone , 20 ml of a 37 % formaldehyde aqueous solution , 50 ml of water and 0 . 7 g of oxalic acid was stirred for 18 hours at room temperature . after working up the reaction mixture , the crude reaction product was purified by column chromatography over polyamide . elution with pentane - dichloromethane 80 / 20 yielded the pure 2 - hydroxymethyl - 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone , which was recrystallized from ethyllactate ; m . p . 124 °- 125 ° c . infrared absorptions ( kbr disc .) were at 3360 , 3170 , 1693 , 1675 , 1607 , 1596 , 1465 , 1300 , 1280 , 1236 , 1220 , 1160 , 1085 , 1050 , 1000 , 950 , 905 , 850 , 770 , 605 , 552 , 506 and 397 cm . sup . - 1 . nmr spectrum [ dmso - d6 ( dimethylsulfoxide , containing 6 deuterium atoms instead of hydrogen ), internal standard si ( ch 3 ) 4 ] had signals at δ = 1 . 25 ( singlet ), δ = 2 . 13 ( singlet ), δ = 3 . 42 ( broad signal ), δ = 5 . 0 ( broad signal ), δ = 8 . 1 ( broad signal ). the mass spectrum showed peaks at m / e 158 , 141 , 140 , 128 , 127 , 115 , 101 , 97 , 85 , 69 , 43 . to a mixture of 1 . 0 g of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone , 5 g of propanal and 20 ml of water were added 0 . 2 g of oxalic acid and the mixture was stirred at room temperature for 25 hours and then extracted three times with chloroform . the chloroform extract was evaporated and the residue purified by column chromatography on polyamide using ether - pentane 10 / 90 as the eluent . pure 2 -( 1 - hydroxypropyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was obtained , which was recrystallized from ether - pentane 50 / 50 ; solid mass at room temperature . infrared absorptions ( kbr disc .) were at 3380 , 3200 , 1695 , 1617 , 1460 , 1440 , 1380 , 1370 , 1365 , 1295 , 1254 , 1215 , 1084 , 1078 , 1009 , 973 , 948 , 731 and 570 cm - 1 . nmr spectrum [ dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at δ = 1 . 25 ( singlet ), δ = 2 . 10 ( singlet ), δ = 3 . 26 ( multiplet ), δ = 4 . 92 ( doublet ), δ = 8 . 03 ( singlet ), δ = 1 . 25 ( multiplet ), δ = 0 . 90 ( multiplet ). the mass spectrum showed peaks at m / e 186 , 157 , 128 , 101 , 97 , 85 , 69 , 57 , 43 . example ix was repeated except that in this instance the propanal was replaced by 5 g of butanal . from the reaction mixture 2 -( 1 - hydroxybutyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was isolated with m . p . 103 °- 104 . 5 ° c . infrared absorptions ( kbr disc .) were at : 3490 , 3150 , 1690 , 1618 ( sh ), 1609 , 1462 , 1435 , 1365 , 1340 , 1272 , 1245 , 1222 , 1090 ( sh ), 1075 , 1050 , 1005 , 982 , 948 , 855 , 760 , 745 , 720 , 689 , 607 , 595 and 586 cm . sup . - 1 . nmr spectrum [ dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at : δ = 1 . 20 ( singlet ), δ = 2 . 05 ( singlet ), δ = 3 . 30 ( multiplet ), δ = 4 . 82 ( doublet ), δ = 7 . 85 ( singlet ), δ = 1 . 0 - 1 . 5 ( multiplet ), δ = 0 . 80 ( triplet ). the mass spectrum showed peaks at m / e 200 , 157 , 139 , 128 , 111 , 101 , 85 , 72 , 71 , 57 , 43 . example ix was repeated , except that in this instance the propanal was replaced by 6 g of octanal . from the reaction mixture 2 -( 1 - hydroxyoctyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was isolated with melting point 97 °- 98 ° c . infrared absorptions were at ( kbr disc . ): 3495 , 3180 , 2960 , 2920 , 2860 , 1690 , 1618 , 1610 , 1460 , 1436 , 1365 , 1335 , 1260 , 1245 , 1205 , 1070 , 1005 , 972 , 945 , 760 , 722 and 578 cm . sup . - 1 . nmr spectrum [ solvent dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at : δ = 1 . 25 ( singlet ), δ = 2 . 10 ( singlet ), δ = 3 . 30 ( multiplet ), δ = 4 . 93 ( doublet ), δ = 8 . 00 ( singlet ), δ = 1 . 20 ( multiplet ), δ = 0 . 85 ( triplet ). the mass spectrum showed peaks at m / e 256 , 195 , 167 , 130 , 129 , 128 , 85 , 84 , 82 , 81 , 57 , 43 . example ix was repeated , except that in this case the propanal was replaced by 4 g of cis - 4 - heptenal . after column chromatography of the reaction mixture the pure 2 -( 1 - hydroxy - 4 - cis - heptenyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was isolated . infrared absorptions ( kbr disc .) at : 3480 , 3200 , 3005 , 1695 , 1615 , 1458 , 1435 , 1370 , 1336 , 1249 , 1240 , 1083 , 1070 , 1004 , 935 , 760 , 720 , 685 and 575 cm . sup . - 1 . nmr spectrum [ solvent dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at : δ = 1 . 21 ( singlet ), δ = 2 . 05 ( singlet ), δ = 3 . 40 ( multiplet ), δ = 4 . 90 ( broad signal ), δ = 7 . 90 ( broad signal ), δ = 1 . 2 - 1 . 5 ( multiplet ), δ = 1 . 7 - 2 . 2 ( multiplet ), δ = 5 . 15 ( multiplet ), δ = 0 . 89 ( triplet ). the mass spectrum showed peaks at m / e 240 , 222 , 179 , 151 , 129 , 128 , 95 , 85 , 84 , 83 , 69 , 68 , 57 , 55 , 43 . example ix was repeated , except that in this instance the propanal was replaced by 5 g of furfural . from the reaction mixture 2 -( 1 - hydroxymethylfuran )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone was isolated by column chromatography as a mixture of two dia stereoisomers in the form of a semi - solid mass at room temperature . infrared absorptions ( kbr disc .) were at : 3440 , 3200 , 1700 , 1617 , 1500 , 1450 , 1370 , 1239 , 1145 , 1074 , 1050 , 1005 and 740 cm . sup . - 1 . nmr spectrum [ solvent dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at : δ = 1 . 05 and 1 . 35 ( singlet ), δ = 2 . 02 and 2 . 14 ( singlet ), δ = 4 . 52 and 4 . 57 ( singlet ), δ = 5 . 50 and 5 . 80 ( broad signal ), δ = 8 . 00 ( broad signal ), δ = 6 . 1 - 6 . 4 ( multiplet ), δ = 7 . 35 and 7 . 50 ( quartet ). the mass spectrum showed peaks at m / e 224 , 128 , 127 , 97 , 96 , 95 , 85 , 57 , 43 . a mixture of 2 . 0 g of 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone , 10 ml of acetone and 25 ml of 6n hydrochloric acid was stirred at room temperature for 48 hours . after working up the reaction mixture , the crude reaction product was purified by column chromatography . elution with pentane - ether 90 / 10 yielded pure 2 -( 2 - hydroxy - 2 - propyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone . infrared absorptions were at ( kbr disc . ): 3480 , 3380 , 1700 , 1686 , 1620 ( sh ), 1610 , 1470 , 1460 , 1445 , 1383 , 1370 , 1256 , 1210 , 1182 , 1118 , 1080 , 1075 , 1003 , 969 , 902 , 860 , 794 , 750 , 565 , 325 and 318 cm . sup . - 1 . nmr spectrum [ solvent dmso - d6 , internal standard si ( ch 3 ) 4 ] had signals at : δ = 0 . 99 ( singlet ), δ = 1 . 12 ( singlet ), δ = 1 . 18 ( singlet ), δ = 2 . 05 ( singlet ), δ = 4 . 32 ( singlet ), δ = 7 . 80 ( broad signal ). the mass spectrum showed peaks at m / e 186 , 171 , 129 , 127 , 101 , 97 , 85 , 71 , 59 , 58 , 57 , 43 . in an aprotic solvent the compound was fully converted to the furenidone upon heating at 160 ° c for 8 minutes . to 200 g or a commercial available frying fat were added 15 mg of 2 -( 1 - hydroxy - 4 - cis - heptenyl )- 2 , 5 - dimethyl - 4 - hydroxy - 3 -( 2h )- furanone and the mixture was heated for 5 minutes at 150 ° c . this fat was unanimously preferred to the fat without addition by the flavour evaluation panel , because of its more sweet , butterlike character .
addition compounds of 2 - or 5 - monoalkyl and 2 , 5 - dialkyl - 4 - hydroxy - 2 , 3 - dihydrofuran - 3 - ones and c 2 - c 9 carbonyl compounds are provided . these addition compounds are useful to impart improved flavouring properties to foodstuffs .