The principal representative of the nitriles is that of formic acid, viz., hydrogen cyanide, HCN. It is formed during the production of the oils of bitter almond and cherry laurel, but also occurs in the distillates of a large number of plants.5)
1) Liebig's Annalen 185 (1877), 37.
2) Report of Schimmel & Co. April 1905, 20. 2) Ibidem April 1904, 70; April 1905, 60.
4) Ibidem April 1909, 95.
5) Verslag omtrent den staat van 's lands Plantentuin te Buitenzorg over het jaar 1889, 29; 1897, 37; Greshoff, Distribution of prussic acid in the vegetable kingdom, British Association, York 1906; Arch, der Pharm. 244 (1906), 397, 665; Weehuizen, Pharm. Weekblad 43 (1906), 907; Guignard, Comptrend. 143 (1906), 451; Herissey, Journ. de Pharm. et Chim. VI. 24 (1906), 350, 537; Jitschy, ibidem 355; Hebert, Bull. Soc. chim. III. 35 (1906), 919; Bertrand, Compt. rend. 143 (1906), 832; Guignard, Bull. Sciences Pharmacol. 13 (1906), 603; Dunstan and Henry, Annal. de Chim. et Phys. 10 (1907), 118; Greshoff, Pharm. Weekblad 45 (1908), 770.
According to data found in phytochemical literature the following plants yield hydrogen cyanide only: Hygrophorus agathomus, H. cerasinus (?), Marasmius oreades, Pholiota radicosa, Russula foetens, Gymnogramme aurea, species of Lastrea and Athyrium, Triglochin palustris, T. maritima, Scheuchzeria palustris, Gly-ceria aquatica, Sorghum halepense, S. nigrum, S. vulgare, St/pa hastricina, St. leptostachya, St. tortilis, Gynerium argenteum, Melica altissima, M. ciliata, M. nutans, M. uniflora, Zea Mays, Briza minor, Lamarkia aurea, Holcus lanatus, Poa pratensis, Festuca Poa, Arum maculatum, Alocasia Veitchii, Colocasia gigantea, Cyrtosperma lasioides, C. Merkusii, Lasia aculeata, L. Zollingeri, Salix triandra (amygdalina), Sponia virgata, Aquilegia chrysantha, A. vulgaris, Thalictrum aquilegifolium, Ranunculus arvensis, R. repens, Nandina domestica, Lepidium sativum (?), Rides aureum, R. rubrum, Grossularia nigrum, Lotus arabicus, L. austral is, Phaseolus lunatus, P. Mungo, Cicer arietinum, Dolichos Lablab, Linum perenne, L. usita-tissimum, Citrus medicaid), Chailletia cymosa, Bridelia ovata, Elateriospermum Tapos, fievea brasiliensis, H. Spruceana, Jatropha angustidens, Manihot Bankensis, M. Glaziovii, M. palmata, M. utilissima, Ricinus communis, Kurrimia ceylanica, Cupania spec, Rhamnus frangula, Sterculia spec, Gynocardia odorata, Hydnocarpus alpina, H. anthelminthica, H. inebrians, Kiggelaria africana, Pangium ceramense, P. edule, Ryparosa cassia, R. longipedunculata, Taraktogenos Blumei, T. tyurzii, Trichadenia ceylanica, Psidium montanum (?), Comb return con-strictum (?), Homalium(Blackwellia) tomentosum, Tacsonia spec, T. Van-Vo/xemii, Modecca Wightiana, Ophiocaulon gummifer, Passiflora alata, P. ccerulea, P. edulis, P. foetida, P. hybrida, P. laurifolia, P. maculata, P. Princeps, P. quadrangularis, P. suberosa, Ipomoea obscura, Isonandra (Bassia) Mottleyana(?), Payena latifolia, Merrem ia vitifolia, Osmohydrophora nocturna(?), Aplotaxis candicans, Centaurea montana, C. solstitial is, Pyrethrum caucasicum, Dimorphoteca pluvial is, Cirsium arvense.
Hydrocyanic acid and benzaldehyde are yielded by the following plants: Pteris aquilina, Pan/cum max/mum, P. muticum, Ximenia americana, Amelanchier alnifolia, A. canadensis, A. vulgaris, Chamaemeles coriacea, Crataegus orientalis, C. oxy-acantha, Eriobotrya japonica, Nuttallia cerasiformis, Osteomeles spec, Photinia arbutiiolia, P. Benthamiana, P. serrulata, P. variabilis, Pyrus americana, P. Aria, P. Aucuparia, P. Cydonia, P. germanica, P. japonica, P. Malus, P. mespilus, P. pinnatifida, P. Ringo, P. spectabilis, P. torminalis, Prunus adenopoda, P. americana, P. Amygdalus, P. alleghaniensis, P. Armeniaca, P. avium, P. Besseyi, P. Capollin, P. caroliniana, P. Cerasus, P. Chamaecerasus, P. divaricata, P. domestica, P. javanica, P. Laurocerasus, P. lusitanica, P. nana, P. occidentalis, P. Padus, P. paniculata, P. pendula, P. pennsylvanica, P. Puddum, P. serotina, P. sphaerocarpa, P. spinosa, P. subhirtella, P. undulata, P. virginiana, P. Persica, Cotoneaster allinis, C. bacillaris, C. buxifolia, C. Francheti, C. frigida, C. horizontal's, C. inte-gerrima, C. microphylla, C. multiflora, C. panosa, C. thymaefolia, Exochorda Alberti, Kerria japonica, Neviusia alabamensis, Pygeum africanum, P. latifolium, P. parvifforum, Spiraea Aruncus, S. japonica, S. r(neiffii, S. Lindleyana, S. prunifolia, S. sorbitolia, Rhodotypos kerrioides, Stranvaesia glaucescens, Indigofera galegoides, Vicia angustifolia, V. canadensis, V. hirsuta, V. macrocarpa, V. sativa, Corynocarpus laevigata, Schleicheria trijuga, Echinocarpus Sigun, Lucuma Bonplandia, L mammosa, L pom if era, Nemecylon spec, Ipomcea dissecta, I. sinuata, I. vitifolia, Gymnema latifolium, Sambucus nigra, Plectronia dicocca, Chardinia xeranthemoides, Xeranthemum annuum, X. cylindricum.
The presence of hydrocyanic acid is ascertained in the ordinary manner by means of the Prussian blue test. To a small amount of the distillate are added first a few drops of caustic soda solution and then a few drops of ferrous sulphate solution containing ferric salt. The mixture is once more thoroughly shaken and acidified with dilute hydrochloric acid. The precipitate of ferrous and ferric hydroxides is thus dissolved and in the presence of hydrocyanic acid, the characteristic blue precipitate of Prussian blue reveals itself. The reaction is so delicate that even the smallest traces of hydrocyanic acid can thus be detected.
For the rapid detection of hydrocyanic acid in a plant the observation .of Mirande1) can be utilized. Under the influence of anaesthetics, such plants as contain hydrocyanic acid in complex combination, set free hydrogen cyanide, the presence of which can be detected by means of sodium picrate paper,2) which is colored red by hydrogen cyanide.
For the quantitative determination of hydrogen cyanide see the chapter on "The examination of volatile oils".
Hydrogen cyanide does not occur as such in most plants but is contained in them in the form of a glucoside, of which amygdalin is the most common.
In plants amygdalin is accompanied by the ferment emulsin, which, in the presence of water, hydrolyses the glucoside to benzaldehyde, glucose and hydrogen cyanide:
C20H27NO11+2H2O = C6H5XHO + HCN + 2C6H18O6.
In recent years much attention has been directed to amyg-dalin and its hydrolysis by means of emulsin. The rather complicated relationship cannot here be discussed. Suffice it to refer to the original literature on this subject.3)
In addition to amygdalin a number of other glucosides are known which upon hydrolysis yield hydrogen cyanide, viz.: coryno-carpin, dhurrin, gynocardin, laurocerasin, linamarin (= phase-olunatin(?), lotusin, manihotoxin, prulaurasin, sambunigrin and vicianin.
Other nitriles occurring in volatile oils are those of phenyl-acetic acid, of phenylpropionic acid and of vinylacetic acid.
1) Compt. rend. 149 (1909), 140.
2) Guignard, Ibidem 142 (1906), 552.
3) Van Rijn, Die Glycoside. Berlin 1900; Walker, Journ. chem. Soc. 83 (1903), 472; Dakin, Journ. chem. Soc. 85 (1904), 1512; Bourquelot and Herissey, Journ. de Pharm. et Chim. VI. 26 (1907), 5; Caldwell and Courtauld, Journ. chem. Soc. 91 (1907), 666, 671; Herissey, Journ. de Pharm. et Chim. VI. 26 (1907), 194, 198; Arch, der Pharm. 245 (1907), 638, 641; Feist, Ibidem 246 (1908), 206, 509; Rosenthaler, Ibidem 365; Auld, Journ. chem. Soc. 93 (1908), 1251, 1276; Rosenthaler, Arch, der Pharm. 246 (1908), 710; Biochem. Zeitschr. 14 (1908), 238; 17 (1909), 257; Auld, Journ. chem. Soc. 95 (1909), 927; Feist, Arch, der Pharm. 247 (1909), 226, 542; Bourquelot, Journ. de Pharm. et Chim. VI. 29 (1909), 576; Tutin, Journ. chem. Soc. 95 (1909), 663; Walker and Krieble, Ibidem 1369, 1437.
Phenylacetic acid nitrile, Benzyl cyanide, C6H5CH2CN, according to A. W. Hofmann, is the principal constituent of, the oil of Tropaeolum ma/us,1) also of that of Lepidium sativum.2) It is probably also contained in neroli oil.
Gadamer3) has since shown that the observations of Hofmann with regard to Tropaeolum ma/us are only conditionally true. When properly distilled, this plant yields benzyl mustard oil. The formation of benzyl cyanide is due to improper mothods. (For further details see the oil of Tropaeolum majus.)
Benzyl cyanide boils at 231 to 232° and at 18° has a specific gravity of 1,0146. When hydrolysed it yields phenylacetic acid, m. p. 77°.
Phenylpropionic acid nitrile, C6H5CH2CH2CN, is the principal constituent of water cress oil (Nasturtium officinale).*) It boils at 261° and when acted upon by alkali is converted into phenylpropionic acid which melts at 47°.
Vinylacetic acid(Crotonic acidjnitrile, Allyl cyanide, CH2:CHCH2CN, traces of which are always found in mustard oil, can be obtained in larger amounts by careless distillation as decomposition product from allyl isothiocyanide. In as much as allyl cyanide is light (d17.5o 0,835), the presence of larger amounts of this substance would be revealed by a depression of the specific gravity of the mustard oil.