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Hugh McGuigan.

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TASTE 209

The hydroxyl group has often been associated with a sweet
taste. Sternberg (Geschmack and Geruch) has pointed out that
in organic compounds, in order to have a sweet taste. the alkyl
groups must not exceed the OH groups, by more than one, or
their combination will be bitter.
Thus Rtamnose: CH3(CHOH)4CHO is sweet,
CH3

(CH0H)3
but methyl rhamnoside CH\ is bitter.

I >

I

OCH,
Again, the sweetness in an homologous series increases with the

CHjOH
increase of hydroxyl groups, e.g. glycol : I

CHjOH

CH2OH

I

is sweet, but not so sweet as glycerol: CHOH

I

CH2OH
and glucose:

CH2OH

(CH0H)4

CHO

is still sweeter. Most substances with the formula (CH20)n
are sweet. That other factors than the OH groups enter into
the production of a sweet taste is shown by the fact that lead
acetate is sweet, yet contains no OH groups; and saccharin,
five himdred times sweeter than cane sugar, contains no OH
groups. Again the corresponding para compound of saccharin
is tastelesss, showing that the architecture of the molecule is
perhaps nfore important than the chemical grouping. It has been
suggested that the stimulation of the taste buds is a physical
process due to intramolecular vibrations, but we have no way of
testing such a suggestion.

Again in those aromatic bodies containing an OH group the
position of this in the ring and the relation to other groups is
interesting, e.g. :



14



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210



OH



OH



CHEMICAL PHABUACOLOaY

OH OH

/\

OH



OH



OH



OH OH



OH



Pyrocatechol Resorcinot


Pyrogallol


Phloroglucinol


(bitter) (sweet) (bitter)


(sweet)


/\


NH2


/ \S02\

^NH


/\


SO,.

)NH


\y


COOH


\ /

Saccharin


NH,


Anthranilic acid


(very sweet) Amino saccharin


(sweet)




' (very;^sweet)


OC2F


I5











SOi



CO



NH.CO.NH2 Br

Para phenetol or Brom saccharin
Dulcin (sweet) (first sweet,

then bitter)



NH



CO.



\



:o/



NH



SO;

CO



-^NH



Phthalimide — ^very similar in com-
position to saccharin — is not
sweet.



NO2
Nitro saccharin]
(very bitter)



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CHEMISTRY OF TASTE 211

This shows that the arrangement of the molecule is of consider-
able importance, but we cannot explain taste in relation to struc-
ture. Saccharin is an orthocompound; resorcin a meta; and
dulcin a paracompound, all of which are sweet. This is further
illustrated by the dififerences in the taste of optical isomers;
dextro-asparagin is sweet while levo-asparagin is not; and dextro-
glutaminic acid is sweet whereas the levo acid is tasteless.

In a recent study of the chemistry of taste, Oertly and Meyers
(Journal of Am. Chem. Society, 1919, vol. 41, p. 855) have worked
out a theory relating to the aliphatic sweet stuffs. They think
that taste is dependent on two factors, or chemical groups, — a
glucophoric and an auxogluc. They define a glucophore as a
group of atoms which has the power to form sweet compounds
by uniting with a niunber of otherwise tasteless atoms or radicals.
An auxogluc is defined as an atom or radical which combined with
any of the glucophores 3rields a sweet compound. Any gluco-
phore will form a sweet compound with any auxogluc.

The following radicals are found to be glucophores in the sense
of their theory:

. 1. -CO— CHOH(+H), -4. CH2OH.CHOH-,

2. CO2H.CHNH2-. 5. CH2ONO2-

3. H3-X 6. H3-X Hj-y
"C — C — C —

nix H.l:e H.ly

The (+ H) in glucophore 1, simply indicates that the group
must be united with one hydrogen atom at least, in order to
become a glucophore.

In the general formula H3-X the abbreviation HI is general

C —
BAs
for chlorine, bromine, and iodine. Flourine derivatives may be
included possibly. The small index (x) refers to the number of-
halogen atoms in the glucophore. It may vary froin one to three,
the number of hydrogen atoms in the glucophore meanwhile
decreasing from two to zero; e.g., methyl iodide has the
glucophore CH2I — . In this case I limits the abbreviation
HI to a singly atom of halogen. The index (x) equals one.



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212



CHEMICAL PHARMACOLOGY



In respect to the hydrogen, the index is 3 — x which is equal
to two, hence CH2I— agrees with the general formula. Chloro-
form has the glucophore — CCls which also agrees with the
general formula. The index (y) has the same significance as
(x) but varies from one to two.

The following atoms or radicals seem to act as auxo-
glucs, yielding with glucophores sweet compounds:

(a) H, hydrogen.

(6) The radicals, CnH2n+iO, of saturated hydrocarbons, con-
taining from 1 to 3 carbon atoms. Example CHaCHa —

(c) The radicals CnHan+iO of monohydric alcohols, n being
equal to one or two. Example CH2OH —

(d) The radicals Cnlian-iOn of polyhydric alcohols. Example
CH2OH.CHOH—

The following tables indicate more clearly the significance of
glucophores and auxoglucs.

Table I.— Glucophore CH2OH— CHOH—

Auxogluc Name of Compound Taste

H— Glycol ' Sweet

CH3 — 1, 2-Propanediol Sweetish

CH3CH2— 1, 2.Butanediol Sweetish

CH2OH— Glycerol Sweet

CnH.2n-i Polyhydric alcohols All sweet

Table II.— Glucophore, — CO.CHOH— H.

H — Gly collie aldehyde Distinctly sweet

CH3 — Oxy acetone Sweet

CH2OH — Glyceric aldehyde Sweet and bitter

monomolecular SUghtly sweet

bimolecular Sweet

Dioxyacetone Sweet
CH3CHOH — .. Methyl-glyceric

aldehyde,

CH3(CHOH)2CHO Sweet and bitter

Methyl-dioxyacetone Sweetish

CnH2n-iOn ... Sugars, e.g. hexoses Sweet



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GLUCOPHORES



213



Table III.— Glttcophore, CO2H— CHNH2

Auxogluc Name Taste

H — Amino-acetic acid Sweet

CH» — dl-a- Amino-propionic acid Sweet

CH3CH2 — dl-a-Amino-butyric acid Sweet

CH8(CH2)2 — dl-a-Amino-n-valeric acid Sweet
CH2OH — . ..... dl-Serine, a-amino-j8-hy-

droxy propionic acid Sweet
CH3CHOH— . dl-a-Amino-/3-hydroxy-bu-

tyric acid Sweet

CnH2n-iOn — • • d-Glucosaminic acid Agreeably sweet



Table IV.— GLtrcoPHORE CH2ONO2



CH3- Ethyl nitrate

CH3(CH2)2n— . . Butyl nitrate

(CH3)2CH— .. Isobutyl nitrate

(CH3)2CHCH2- Isoamyl nitrate

CH2OH — Glycol mononitrate



Sweet

Sweet

Sweet

Sweetish

Sweet



H3-.2
Table V. — Glucophore C

HU

H — Methyl chloride Sweetish

Methylene chloride SWeetish

Chloroform Sweet

Bromoform Sweetish

Iodoform Sweetish

CH3 Ethyl chloride Sweetish

Ethyl bromide Burning

CH2OH — Ethylene chloro hydrine Sweet



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214



CHEMICAL PHAKMACOLOGY



H3-. N^



Table VI — Gltjcophore C

H — Ethylene chloride

Ethylene bromide
Ethylene chloro-iodide

CHj — 2-ChIoro-i-iodopropane

CH2OH— 2, 3-Dichloro-i-hydroxy—

propane
2, Chloro-3-bromo-
propanei-ol



— C —

HI, Bly

Sweetish
Sweetish
Sweet
Sweet

Burning spicy

Sweet



XXIV. TANNIC, DIGALLIC ACID, OR GALLOTANIC ACID



C14H10O29, or
CO



-O



HO



OH HOOC



OH

occurs in large quantities

OH



OH



in gall nuts and in all kinds of bark, especially oak. It is the ac-
tive coxistituent of all vegetable astringents. Its pharmacologic
action is the same as that of metalUc astringents and is due to a
union with, and precipitation of, proteins. Tannic acid is soluble
in water, alcohol, or ether. When boiled with H2SO4 it is com-
pletely converted into two molecules of gallic acid which shows
that it is a gallic acid anhydride,

OH

OH

C14H10O9+ H2O ->2

onk ycooH

Gallic acid



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TANNINS 215

though it is not known which OH group unites with the carboxyl
in the synthesis. All tannins, tannic acid, and gallic acid are
reducing agents, and because of this it was formerly thought
that they were all glucosides. It is now known that not all of
them are e.g. pure tannic acid. Ordinary tannin, is impure tannic
acid and on hydrolysis yields 7-8 per cent, of glucose. The com-
position varies, in some, tannins having been found to be the
penta digallic ester of glucose.

CH2— t

I
CHO— t

I
CH

I
yCHO — t "f represents tannic acid.

/ \
OC CHO— t

\l
^CHO

The composition of many tannins has not been determined.

Tannic acid unites with albiunin and is an alkaloidal reagent,
while gallic acid is not. Animal skins properly treated with it
are tanned. Tinctures were formerly detannated by shaking
with finely ground animal hides, but this method has been
given up. Tannin forms inks with iron salts, and for this rea-
son, tannins and iron salts are incompatible. According to
the color of the ink so formed, tannins have been divided into,
two classes, first — the pyrogallol class, which gives a dark blue
color, and second — the catechol class which gives a greenish
color.

Tannins differ in the tendency to unite with proteins. A de-
coction of tea is a much more efficient precipitant than a similar
decoction of coffee.



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216



CHEMICAL PHABIIACOLOOY



On heating gallic acid COt is given off and pyrogallol
formed. —



OH



OH



OH
OH



/\0H



COOH



+ CO2



OH



Gallic acid



Pyrogallol



All taniuns absorb oxygen readily, but pyrogallol does so to a
much greater extent.

Tannic acid is used in medicine for its astringent properties:
externally in cases of local sweating or weeping ulcers, and to
harden the skin. Lead, zinc, and alum salts are used for the same
purpose. In inflammations of the throat, it is used in lozenge
form as an astringent. In cases of diarrhoea it is used in the form
of tinctures of Kino, Krameria, Gambir, Catechu, etc. Its ac-
tion in these cases is due to a combination with the material in
the gut and also to a similar action on the gut wall, which it
protects. It is used as an antidote in cases of poisoning with
alkaloids ahd Heavy metals with which it combines. In such
cases the precipitated material must be removed or the combina-
tion is digested in the body and the action of the alkaloid is
only delayed and not avoided. This delay however may pre-
vent an action by the drug, since such delay may enable the body
to oxidize or excrete it as fast as it is absorbed. In some indi-
viduals, with an idiosyncrasy, tannic acid induces local irritation
and inflammation.

FATE IN THE BODY

When tannic acid is taken internally most of it, in some cases
all, is oxidized. Traces may be excreted in the urine, and feces.
It does not exist in the tissues as such but as the gallate or tannate
of sodium. These are devoid of astringent effects. According
to Harnack, pyrogallol is sometimes formed from gallic acid in
the urine.



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TANNINS 217

Tests for Tannin

1. Test the solubility of tannic acid in water, alcohol, ether,
chloroform. Repeat with gallic acid.

2. Add a solution of ferric chloride to tannic acid. Lead ace-
tate added to tannic acid produces a white precipitate; if NaOH
is added to this and the mixture shaken, a pink color is formed.

3. Add tannic acid to a solution of albimiin (a) excess albumin;
(6) excess tannic acid; (c) potassimn hydFOxide. Repeat with
gallic acid.

4. Neutralize a solution of tannic acid with KOH solution.
Add to this neutral solution albumin and compare the result with
that obtained in 3.

5. Add tannic acid to a solution of 1 per cent, quinine bisul-
phate. Repeat with 0.1 per cent, strychnine sulphate.

6. To a 1 per cent, solution of galUc acid add a few drops of 1
per cent. KCN, and there will appear a red color which soon
fades but reappears on shaking (Young's te^t). Pure tannic
acid does not give this reaction.

7. Boil 1 gm. tannin 15 minutes with 10 cc. of 5 per cent..H2S04.
NeutraUze and apply Fehhng's test. What is the result?
Meaning?

8. Permanganate solutions oxidize tannic acid. To 5 cc.
tannic acid solution add drop by drop KMn04 and note
results. This fact is used in the quantitative determination of
tannin. This is illustrated in the following method — Procter's
Modification of LowenthaJs — ^f or the determination of tannin in
tea.

(A) Preparation of Reagents

1. Potassium permanganate. Make up a solution containing
1.33 grams per liter.

2. Tenth-normal oxaUc acid. Make up a solution containing
6.3 grams per Uter.

3. Indigo carmine. Make up a solution containing 6 grams
of indigo carmine (free from indigo blue) and 50 cc. of concentrated
sulphuric acid per liter.

4. Gelatin solution. Prepare by soaking 25 grams of gelatin
for one hour in a saturated sodium chloride solution, heat until
the gelatin is dissolved, and make up to 1 liter after cooling.



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218 CHEMICAL PHARBiACOLOGY

5. Mixture. Combine 975 cc. of saturated sodium chloride
solution and 25 cc. of concentrated sulphuric acid.

6. Powdered kaolin.

(B) Determination

Obtain the value of the potassium permanganate in terms of
the oxaUc acid. Boil 5 grams of the tea for half an hour with 400
cc. of water; cool, transfer to a graduated 500 cc. flask, and make
up to the mark. To 10 cc. of the infusion (filtered if not clear)
add 25 cc. of the indigo carmine solution and about 750 cc. of
water. Add from a burette the potassimn permanganate solu-
tion, a Uttle at a time while stirring, until the color becomes light
green, then cautiously, drop by drop, imtil the color changes to
bright yellow or, further, to a faint pink at the rim. The number
of cubic centimeters of permanganate used furnishes the value
(a) of the formula given below.

Mix 100 cc. of the clear infusion of tea with 50 cc. of gelatin
solution, 100 cc. of salt acid solution, and 10 grams of kaolin,
and shake several minutes in a corked flask. After settling
decant through a filter. Mix 25 cc. of the filtrate (corresponding
to 10 cc. of the original infusion) with 25 cc. of the indigo solution
and about 750 cc. of water, and titrate with permanganate. The
amount used gives the value b; a — b = c; c equals the amount
of permanganate required to oxidize the tannin. Assume that
0.04157 gram of tannin (gallotannic acid) is equivalent to 0.063
gram of oxalic acid.

XXV. NEUTRAL PRINCIPLES

These are physiologically active substances which are neither
acid nor basic and have no distinguishing chemical properties.
Some are bitter and could, therefore, be classified as bitters,
except for their toxicity and pharmacologic actions. They re-
semble the glucoside closely, but on hydrolysis do not decompose
into sugar; although santonin sometimes contains sugar as an
impurity. The classification of neutral bases, therefore, is in-
definite and includes those chemically nondescript principles of
neutral reaction which are physiologically active. Digitalis,
strophanthus, and even alkaloidal salts from the chemical stand-
point might be included, except that they have chemical proper-



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NEUTRAL PRINCIPLES



219



ties that place them in more sharply defined chemical groups.
The chief neutral principles are:

1. Santonin

2*. Picrotoxin

3. Elaterin

4. Chrysorobin

Santonin, CibHisOs, is obtained from wormseed and forms as
crystalline, colorless, bitter, shining leaflets, which melt at 170**C.,
and are soluble in 500 parts of cold water. It is used as an anthel-
mintic, especially for roundworms.

It is the internal anhydride (lactone) of santonic acid.

CHs H2




=



H— OH



H— CH.COOH



CH.8 CH2
Santonic acid



CHs



Cxls 1X2



H.



=



\




H— O



-CH



>



CO



CHs

Santonin
Santonin is a ketone and as such, will react with phenyl hydra-
zine and hydroxylamine. When used as an anthelmintic a
sUght amount is absorbed and oxidized to oxysantonin C12H18O4.
Jafife found this substance in the urine of dogs to the amoimt of
5 per cent, of the santonin administered. In rabbits only a
small amoimt could be found. In the rabbit's urine beta-oxy-
santonin was found which is isomeric with alpha-oxysantonin.
After therapeutic doses (0.06 gram) of santonin human urine is
reddish and on the addition of KOH, it becomes carmine.



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220 CHEMICAL PHARBiACOLOGY

On treatment with lime water, the urine becomes a scarlet or
pxirple color.

TESTS

1. Santonin heated with an alcoholic solution of KOH gives a
carmine color, which soon fades tfirough yellow to colorless.

2. Santonin heated with concentrated H2SO4 containing a
drop of ferric chloride becomes pink; 10 milligrams of santonin
to 1 cc. of the acid is sufficient.

PICROTOXIN

Picrotoxin, C80H84O18 is the poisonous principle of cocculus
indicus. It crystallizes in long colorless needles, M.P. 200°C.
It has a very bitter taste, and has a marked action on the medulla
producing spasms that have some resemblance to strychnine
tetanus. Heated to boiUng with 20 times its volume of benzene
or chloroform, it decomposes into picrotoxin and picrotin,

C30H34O18 = C15H16O6 + CisHisOt

The fate of picrotoxin in the body and the manner of its excretion
is unknown.

TESTS

1. Picrotoxin reduces FehUng's solution. Dissolve a little in
a test tube by the aid of dilute NaOH, and add to dilute boiling
Fehling's solution.

2. If it is warmed with a dilute solution 1 per cent. AgNOs
containing slight excess of ammonium hydroxide a black precipi-
tate of metallic silver will be produced. Where only traces of
picrotoxin are present, the precipitate is colored brown.

3. On oxidation with a trace of H2SO4 on a porcelain dish,
picrotoxin becomes orange red and dissolves to a reddish yellow.

4. H. Meltzer's Test. — One to two drops of a mixture of ben-
zaldehyde and absolute alcohol added to some picrotoxin powder
on a watch glass, will produce a red color when a drop of concen-
trated H2SO4 is added. The alcohol here is added as a diluent
because H2SO4 produces a brown color with pure benzaldehyde.
20 per cent, benzaldehyde in absolute alcohol is enough.



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CHRYSOROBIN



221



5. Langley's Test.— Picrotoxin mixed with about 3 times its
weight of KNO3 and moistened with a trace of H2SO4 will give
an intense red color when an excess of strong NaOH is added. '

6. Physiologic Test. — Typical convulsions are produced in the
frog, but they differ in many respects from those caused by
strychnine. Picrotoxin spasms cease when the medulla is
removed while strychnine tetanus continues after ablation of the
medulla.

ELATERIN

Elaterin, C20H28O5, is the neutral principle of elaterium. It
consists of two substances, alpha-elaterin, which is levo-rotary
and inert, and beta-elaterin, the active dextro-rotary substance.

Elaterin does not exist as such in fruit, but is formed after
expression by a diastatic ferment acting on a glucoside. Little
is known of the chemistry of elaterin or its fate in the body.

CHRYSOROBIN

Chrysorobin is a mixture of neutral principles from Goa
powder. The chief principle is chrysophanolanthranol Ci6Hi208,
m.p. 204**, an orange yellow, tasteless, odorless powder, very
irritating to mucous membranes.

According to Tutin and Clewer, chrysophanic acid has the
formula




or dioxmethyl anthraquinone.



Chrysorobin is the anthranol corresponding to chrysophanic acid
and has the formula



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222



CHEMICAL PHAKMACOLOGY

CH» OH OH



OH OH

Anthrajiol is oxyanthracene
OH



Anthranol

Commercial Goa powder contains a mixture of neutral principles,
C8oH2«07 and in addition to these described, contains dichiysoro-
bin C80H28O7 and its methyl ester. Aloin and salicin have been
classed as neutral principles but they belong definitely to the
glucosides.

In the body part of the absorbed chrysorobin is oxidized to
chrysophanic acid, but most of it is excreted imchanged by the
kidneys and may cause nephritis. In man slight albiuninuria
has been observed after its application to the skin.

XXVI. ALKALOIDS

NITROGEN BASES; PLANT BASES OR ALKALOIDS

These are all synonymous terms and not sharply defined. The
property of N in some compounds to change its valence from 3
to 5, and to unite with acids to form salts is the reason for the
term nitrogen base. The isolation of a number of such bases
from plants, led to the term vegetable alkaloids or "plant bases,"
a term which was formerly restricted to those bases in which the
nitrogen was in combination of pyridine, quinoline, or isoquino-
line. This excluded many nitrogen bases of obvious alkaloidal



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ALKALOIDS



223



reactions, including the caffeine or purine bases, which are now
generally conceded to be alkaloids. Alka- loid means an alkali-
like substance. For convenience of study, nitrogen bases or al-
kaloids in the broad use of the term may be divided as. follows:



(1) Vegetable alkaloids
derivatives of . . .



(2) Animal bases or
Alkaloids . . .



(3) Ptomaines or putre-
factive alkaloids.



(4) Purine Bases

also included under
1.



Nature of Nucleus
Group 1. Pyrrole



Group 2.
Group 3.



Pyridine
Diheterocyclic,
with a common
nitrogen atom



Examples
Hygrine
Stachydrine
Coniine



Atropine,

Sparteine

Strychnine

Papaverine

Pilocarpine

Cafifeine



Group 4. Quinoline
Group 5. Isoquinoline
Group 6. Glyoxaline
Group 7. Purine
Group 8. Cyclic or acyclic

derivatives of

aliphatic amines ChoUne, ar-
ginine
Group 9. Alkaloids of \m-

known constitution

Epinephrine — a catechol or

pyrocatechol derivative.

Choline

Muscarine

Betaine

Neurine

Trimethyl amine.

Parahydroxylethylamine and

other ergot amines.

Purine

Hypoxanthine

Xanthine

Guanine

Theobromine

Cafifeine

Uric acid



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224 CHEMICAL PHARMACOLOGY



(5) Artificial Bases
or synthetic alka-
loids.



Antipyrine
Epinephrine
Cocaine substitutes



In describing these we will not follow this order in detail.

GENERAL CHARACTERISTICS OF ALKALOIDS

1. All alkaloids contain C, H, and N, most of them 0, also*
Those containing 0, are solid and crystalline, while those lacking
O, are liquid and volatile. The liquid and volatile alkaloids may
be regarded as amines, or substituted ammonias and the solid
and crystalline, as amides. See test for N, p. 8.

2. All true alkaloids have an alkaUne reaction. Th^piuine
bases are neutral, to litmus.

3. All have a bitter taste.

4. Most of them have marked physiologic or toxic properties.

5. They form salts by direct addition, as ammonia does.

6. The free alkaloids are relatively insoluble in water and
soluble in ether, chloroform, carbon bisulphide, etc. The salts
have opposite solubilities, thfey are soluble in water, insoluble
in ether, chloroform, carbon bisulphate and the like.

7. The majority are optically active, and turn the plane of
polarized light to the left. A few, coniine, pelleterine, lau-
danosine, and pilocarpine are dextrorotary.

8. They are precipitated by a large number of bodies, which
because they are much used for this purpose, are called alkaloidal
reagents. The most important are:

1. Iodine in KI (Lugol's solution)

2. Hglj in KI (Meyer's reagent)

3. Tannic acid

4. Phosphotungstic acid

5. Gold chloride

6. Platinum chloride

7. Picric acid

8. Picrolonic acid

The shapes etc. of the salt crystals, aid in the identification
of the alkaloid.

9. Many give color changes on being oxidized with nitric
acid, potassium chlorate, potassium bichromate, etc. These
color reactions may be characteristic.



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AMINES



225



10. Since all contain N, they will give the tests for N.
'11. In cases of poisoning, they leave no characteristic post
mortem change.

CHEMISTRY OF ALKALOIDS

The vegetable alkaloids are related to ammonia and nearly
all are tertiary amines. The basicity of the alkaloids, like am-
monia, is due to the property of nitrogen, changing its valence
from 3 to 5. This is illustrated in the formation of ammonium
chloride.

/H



H



N^



H + HCl =




H



The alkaloids form salts in a similar way.

XXVn. AMINES OR SUBSTITUTED AMMONIAS

Amines are derivatives of ammonia in which the hydrogen has
been replaced by alkyl groups. Depending on whether one,
two, or three hydrogens are replaced, the amines are named
primary, secondary or tertiary.





/CH,
^H


/CHa
N^CHa
^H "


/CHs

N^CHs

^CHs




Methy-


Dimethyl-


Trimethyl-




lamine


amine


amine




(primary


(Secondary


(Tertiary



amine)



amine)



amine)



It is hard to draw a sharp dividing line between the simple
amines and the alkaloids.

Secondary and tertiary amines are also known in which the
N takes part in the formation of a ring. For example, in pyridine



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