An Introduction to the Chemistry of Plant Products
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mije ^. p. ^tU pkarg ^ortlj Carolina ^fcttc flInllEgE AN INTRODUCTION TO THE CHEMISTRY OF PLANT PRODUCTS PAUL HAAS D.Sc, Ph.D. LECTURER ON CHEMISTRY, ROYAL GARDENS, KEW, AND IN THE MEDICAL SCHOOL OF ST. MARY'S HOSPITAL, LONDON ; FORMERLY DEMONSTRATOR OP CHEMISTRY AND TOXICOLOGY IN THE MEDICAL SCHOOL OF ST. THOMAS'S HOSPITAL, LONDON T. G. HILL A.R.C.S., F.L.S. READER IN VEGETABLE PHYSIOLOGY IN THE UNIVERSITY OF LONDON, UNIVERSITY COLLEGE; FORMERLY LECTURER ON BOTANY AT THE GOLDSMITHS' COLLEGE AND ON GENERAL BIOLOGY IN THE MEDICAL SCHOOL OF ST. THOMAS'S HOSPITAL, LONDON WITH DIAGRAMS SECOND EDITION LONGMANS. GREEN AND CO. 39 PATERNOSTER ROW, LONDON FOURTH AVENUE & 30th STREET, NEW YORK. BOMBAY, CALCUTTA, AND MADRAS I917 PREFACE TO THE SECOND EDITION. The great advances made in the chemistry of Plant Pigments since the issue of the first edition have neces- sitated the re-writing of the section dealing with this subject. For the rest, we have confined ourselves to making a few minor additions and corrections and adding a number of further references to the literature. P. H. T. G. H. July^ 191 6. a\> K^''^^ Q< s PREFACE TO THE FIRST EDITION, The importance to the botanist of a working knowledge of chemistry can hardly be overestimated, since vege- table physiology is replete with problems awaiting solution by the combined application of botanical and chemical methods. Teachers of vegetable physiology, however, not in- frequently find that their students' knowledge is deficient in just those branches of chemistry which are of parti- cular importance to the botanist, which is, no doubt, largely due to the fact that those compounds which are of interest to the botanist do not necessarily fit into the scheme of instruction of the chemist. The present work is an attempt to provide such students, who are assumed to have some acquaintance with chemistry, with an introductory account of the chemistry and biological significance of some of the more important substances occurring in plants. In compiling this book various sources of informa- tion have been laid under contribution, and although the point of view is, in the main, purely chemical and botanical, the economic aspect has not been lost sight of, and, where possible, mention has been made of the uses of plant products and of the manufacturing processes employed in their preparation. R H. T. G. H. Decetnber, 19 12. CONTENTS. PAGE PREFACE V SECTION I.—FATS, OILS, AND WAXES. PHOSPHATIDES . i Fats I Occurrence .......... i Industrial uses of fats oils vegetable and .... 3 Constitution 5 Extraction .......... 10 Physical properties 11 Chemical properties . 12 Saponification . .13 Chole'^terol and Phytosterol 15 Spontaneous changes in fats ....... 18 Rancidity 18 Drying and resinification ....... Ig General properties and reactions of fats 20 Special tests for particular classes of fats 21 Colour reactions 22 Microchemical reactions 23 Quantitative estimation ......... 24 Quantitative methods for the characterization of fats ... 28 Physiological significance ........ 35 Waxes 43 Phosphatides, Lecithins, or Phospholipines 44 Occurrence -44 Preparation 45 Reactions and characteristics 46 Choline 47 Formation of Lecithin 49 Physiological significance ........ 50 SECTION II.— CARBOHYDRATES 52 Classification 52 Constitution and isomerism of sugars ....... 54 Genera] reactions of sugars 56 Monosaccharides , 57 Pentoses 57 General properties ......... 57 Properties of individual pentoses .59 Hexoses 60 Glucose or dextrose , . 60 Preparation .....,,.,, 60 CON TK NTS PACK Properties "61 Reactions .......... 61 Microchemical tests ........ 63 Levulose or Fructose 64 Properties .......... 65 Reactions .......... 65 Sorbose ........... 65 Galactose 65 Preparation 66 Properties 66 Detection 66 Mannose ........... 67 Detection 67 Disaccharides 68 Cane sugar, sucrose or saccharose 68 Properties and reactions 70 Maltose 71 Properties and reactions ....... 72 Isomaltose ........... 73 Cellobiose .73 Mycose or trehalose ......... 73 Agavose and lupeose ......... 73 Lactose or milk sugar 74 Trisaccharides 74 Raffinose . 74 Detection 75 Melecitose 76 Sugars of unknown molecular weight or sugar-like polysaccharides . 76 Estimation of sugars .......... 77 Volumetric methods ......... 77 Estimation by means of Fehling's solution .... 77 Estimation of pentoses 78 Estimation of glucose 79 Estimation of galactose and mannose .... 80 Estimation of cane sugar ...... 81 Estimation of maltose 81 Estimation of mixtures of sugars ..... 82 Estimation by means of Pavy's solution .... 83 Estimation by Benedict's solution 85 Gravimetric methods ......... 86 Estimation of pentoses 86 Estimation of glucose 88 Estimation of glucose as osazone ..... 92 Polarimetric methods 93 Polysaccharides ........... 96 Classification .......... 96 Starches 97 Starch or amylum 97 Preparation 98 Properties . ........ 99 Action of acids on starch ...... 102 Action of malt or diastase on starch . 103 Action of bacteria on starch ...... 103 Reactions 104 Estimation . 105 CONTENTS ix PAGE .Dextrins io6 General properties log Amylodextrin log Erythrodextrin no Commercial dextrin no Glycogen no Preparation 112 Properties nj Identification 114 Estimation 114 Paradextrane and paraisodextrane 114 Inulin 114 Preparation 117 Characters 118 Identification 118 Inulin-like substances 120 Mannane i2o Paramannane 121 Carubin 121 Galactane 122 Paragalactane 122 Amyloid 123 Gums 123 Microchemical reactions 124 Gum arabic . 125 Reactions 125 Gum tragacanth 126 Wood gum and cerasin or cherry gum 126 Wound gum 126 Mucilage 127 Function 128 Pectic bodies 128 Microchemical reactions 130 Cellulose 131 Classification 131 Characteristics and properties of normal cellulose . 133 Action of chemicals on cellulose 134 Characteristics and properties of compound celluloses . 137 Constitution 139 Industrial uses of cellulose and cellulose products .... 141 Commercially valuable derivatives of cellulose .... 141 Microchemical reactions 144 The synthesis of carbohydrates in green plants 146 Introductory : Aldehydes 146 Formaldehyde 151 Photosynthesis 154 SECTION III.—GLUCOSIDES 169 Constitution 170 Identification 172 Physiological significance 173 Cyanogenetic glucosides 176 Isolation 178 Chemistry ........... 178 Reactions 179 X CONTENTS PAGE Amygdalin i8i Dhurrin 182 Phaseolunatin 182 Lotusin 183 Saponins 183 General properties and uses 183 Solubility 184 * Physiological action 185 < Chemistry 185 Reactions 187 Other glucosides 187 Sinigrin ........... 187 Preparation . 187 Coniferin 188 Salicin 189 Preparation 189 Indicane . • 191 Identification 191 SECTION IV.—TANNINS 193 Occurrence ... ......... 194 Microchemical reactions 197 Chemistry ............ 200 Pyrocatechol, catechol, or pyrocatechin 201 Reactions 202 Resorcinol 202 Reactions 202 Hydroquinone ........... 202 Reactions 202 Protocatechuic acid 203 Reactions 203 Pyrogallol or pyrogallic acid ........ 204 Reactions 204 Phloroglucinol ........... 204 Reactions 205 Gallic acid 205 Reactions 206 Ellagic acid 206 Reactions ........... 207 Phlobaphenes 208 Tannins as glucosides 208 Classification of tannins 209 Properties and description of individual tannins ..... 2H Pyrogallol tannins ......... 211 Gallotannic acid ......... 211 Extraction ......... 213 Reactions 214 Detection of gallic acid in presence of gallotannic acid . 214 Constitution ......... 214 Ellagitannic acid 216 Pyrocatechol tannins 216 Catechu tannic acid 216 Catechin 217 Quercitannic acid 217 Physiological significance of tannins ....... 217 CONTENTS XI PAGE SECTION v.—PIGMENTS 225 Chlorophyll 225 Constitution ........•• 231 Action of alkalies 232 Action of acid 233 Crystalline and amorphous chlorophyll 233 Relationship between chlorophyll and haemoglobin . 236 Extraction of chlorophyll ........ 238^^. Carotinoids or yellow pigments accompanying chlorophyll . 241 Carotin- 242 Xanthophyll 243 Fucoxanthin 243 Anthoxanthins ........... 244 Flavones and Xanthones ......... 244 Yellow colouring matters derived from flavone .... 245 Yellow colouring matters derived from xanthone .... 246 Properties of anthoxanthins ........ 247 Anthocyanins, Phycoerythrin, and Phycophaein ..... 248 Connection between anthocyanins and anthoxanthins . -251 Extraction of anthocyanins ......... 251 Anthocyanins 252 Properties .... ....... 254 Reactions 256 Physiological significance ........ 256 Phycoerythrin 258 Preparation 259 Reactions 259 Phycophaein 260 SECTION VI.—NITROGEN BASES 263 Alkaloids 265 Classification 256 Properties 269 Reactions 270 Isolation 271 Origin of alkaloids in the plant 272 Ptomaines ............ 274 Purine bases ........... 276 Physiological significance of nitrogen bases 280 SECTION VII.—COLLOIDS 283 Properties ............ 284 Diffusibility 284 Optical properties 285 Change of state or gel formation 287 Protective power .... ...... 291 Classification of Colloids ......... 291 Properties of suspensoids . ...... 292 Properties of emulsoids 293 The nature of gels 294 Adsorption ........... 295 Enzyme action ol colloids ........ 297 Xll €NTENTS PAGE SECTION VIII.—PROTEINS 3°! General properties 302 Microchemical reactions 308 Proteins as colloids 308 Decomposition products ......... 313 Amino acids obtained as cleavage products of proteins . -315 Constitution of the protein molecule 3^8 jk^ Polypeptides 3^9 B Occurrence of amino acids in plants 321 Classification of protems 322 Comparison between vegetable and animal proteins .... 328 Extraction ot proteins 330 Synthesis of proteins in the plant 333 Synthesis of amino acids in the plant 337 Estimation