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amic acid, being also formed from dianisbenzhydroxylamine,
while the bcnzdianishydroxylamines are resolved into anisic acid
and bcnzanishydroxamic acid.

The dibenzanishydroxylamines under the same circumstances
yield benzanishydroxamic acid, and not, as might have been
expected, a compound metameric with this :

NO.CO.C 6 H 5

C H,cr +2KOH =

\O.CO.C 7 H 7



C 6 H 5 .C<; + KO.CO.C 6 H 5 + H 2 0.

\O.CO.C 7 H 7

Lessen assumes that the decomposition first proceeds in this
way, and that the-compound formed changes into :

X/ NO.CO.C 7 H 7 O



" A similar exchange between a metal and an acid radical has
often been observed."



DIHYDROXYBENZYL AND DIHYDROXY-
BENZOYL COMPOUNDS.

2190 Protocatcchuicaldehyde, or a-Orthodihydroxybenzaldehyde,
C 6 H. i (OH) 2 CHO.(COH : OH : OH = 1 : 3 : 4), was first prepared
from piperonal (p. 347) and from vanillin or its methyl ether.
Tiemann and Reimer found that it is also formed by the action
of chloroform on an alkaline solution of catechol. 1 In order to
prepare it> a solution of 10 parts of the latter in 600 parts of 16
per cent, caustic soda solution is heated for 5 6 hours with 100
parts of chloroform in an apparatus connected with an inverted
condenser, acidified with hydrochloric acid, allowed to cool,
filtered from a black resinous substance and shaken out with
1 Ecr. Dcutsch. Chem. Gas. ix. 12C9.



344 AROMATIC COMPOUNDS.

ether. The aldehyde is extracted from the ethereal solution by
means of acid sodium sulphite, liberated by dilute sulphuric
acid, again dissolved in ether and the residue on evaporation
re-crystallized from boiling toluene. 1

It is readily soluble in water, alcohol and ether, very slightly
in cold, more readily in boiling toluene, and crystallizes from
water in flat, lustrous needles, melting at 150. Ferric chloride
added to its aqueous solution produces a green colouration, which
becomes first violet and then red on the addition of sodium
carbonate. Ammoniacal silver solution is immediately reduced
by it.

Vanillin, C 6 H 3 (OH)(OCH 3 )CHO(CHO : OCH 3 :OH = 1 : 3 : 4).
The crystalline coating of vanilla (givre de vanillc) was mistaken
by Buchholz for benzoic acid, and by other chemists for cinnamic
acid, although Bley had previously pointed out that it is a
distinct substance. Gobley, who at first took it for cumarin,
subsequently found with V^e, that it differs from this substance,
and named it vanillin, 2 while Stokkebye, who obtained analytical
results differing from those of Gobley, termed it vanillaic acid. 3

The correct formula of vanillin was determined by Carles, who
investigated its properties and some of its derivatives, 4 without
being able to determine its relations to any known compounds.
Tiemann and Haarmann, however, were successful in this, and
prepared it artificially from coniferin, C 1C H 12 8 . This compound
occurs in the cambium sap of the fir-tree, and is decomposed by
emulsin in the presence of water into grape sugar and the
compound C 10 H 12 O 3 , forming odourless crystals, which after
standing in the air for some time have a faint smell of vanilla ;
Tiemann and Haarmann therefore oxidized it with chromic acid
and thus obtained vanillin. On fusion with caustic potash it is
converted into protocatechuic acid, and on heating to 200 with
hydrochloric acid is decomposed into methyl chloride and proto-
catechuicaldehyde, proving that it is the methyl ether of the
latter. 5

Reimer and Tiemann then obtained it by heating guaiacol
(Part III. p. 152) with caustic soda and chloroform, 6 the iso-
meric metamethoxysalicylaldehyde being simultaneously formed
(Tiemann and Koppe). 7



1 Tiemann and Koppe, JScr. Dcutsch. Chcm. Ges. xiv. 2015.

" Jahrcsber. Chcm. 1858, 534. 3 Ibid. 1864, 512.

4 Bull. Soc. Chim. xvii. 2. 5 Ber. Dcutsch. Chem. Ges. vii. 608.

c Ibid. ix. 424. ? Ibid. xiv. 2023.



VANILLIN. 345



The decomposition product of coniferin, referred to above, is
coniferyl alcohol, C 6 H 3 (OH)(OCH 3 )CH=CH.CH 2 OH, and its
conversion into vanillin by oxidation may readily be under-
stood. The latter is formed in a similar manner from eugenol,
C 6 H 3 (OH)(OCH 3 )CH CH.CH 3 , a substance which is found in
oil of cloves.

Vanilla contains 1*5 2'5 per cent, of vanillin and a little
vanillic acid, C 6 H,(OH)(OCH 3 )CO 2 II, but no other aromatic
compounds. 1 Vanillin also occurs in Siam benzoin, 2 in Asa
fcetida* and frequently in small quantities in beet-sugar, 4 since
the sugar beet contains coniferin, which has also been found,
together with vanillin, in asparagus. 5

It is best obtained from coniferin. The trees containing this
substance, Abies cxcelsa, A. peclinata, Pinus strobus, P. cembra,
Larix europaea, and other pines and firs, are felled during the
spring or early summer. The trunks are then sawn into pieces
and freed from bark, the cambium sap being removed by
means of a sharp knife. This is boiled with water, freed from
albumen, and the clear liquid evaporated to one-fifth of its bulk.
The crystals which separate after some time are filtered off,
pressed and re-crystallized after having been boiled with animal
charcoal.

The aqueous solution is then allowed to flow into a warm
mixture of potassium dichromate and dilute sulphuric acid,
the whole being heated for several hours in a flask con-
nected with an inverted condenser. After cooling, the solution
is filtered to remove a small quantity of a resinous substance
and extracted with ether. On evaporation a yellow oil is left,
which solidifies after some days to crystals which are boiled with
animal charcoal and re-crystallized from hot water. 6

Vanillin can also be readily obtained by replacing the nitroxyl
group in paranitromethylmetahydroxybenzaldehyde by hydroxyl,
by the oxidation of ferulaic acid, C 6 H 3 (OH)(OCH 3 )CH 2 .CO 2 H,
which can be prepared on the large scale without difficulty, 7 and
from olivil, 8 C U H 18 5 , the crystalline constituent of the Lecca
gum, or resin of the wild olive, which is used in Italy as

Tiemann and Haarmann, Ber. Dcutsch. Chem. Ges. viii. 1118 ; ix. 1287.

Jannasch and Rump, ibid. xi. 1635.

E. Schmidt, ibid. xix. Ref. 705.

Scheibler, ibid. xiii. 335 ; Lippmann, ibid. xiii. 662.

Lippmann, ibid. xvi. 44 ; xviii. 3335.

Tiemann and Haarmann, ibid. vii. 609 and 614.

7 M. Ulrich, ibid, xviii. Rcf. 682.

8 Schcidcl, ibid, xviii. 685.



34(5 AROMATIC COMPOUNDS.

incense. 1 This substance will be further described along
with eugenol.

Properties. Vanillin forms white needles, generally occurring
in stellate aggregates, which possess a very strong taste and smell
of vanilla. It melts at 80 81, sublimes readily, boils at 285
without decomposition when heated in an atmosphere of carbon
dioxide, and dissolves in 90 100 parts of water at 14, and in 20
parts at 75 80. It is scarcely soluble in cold, more readily in
hot petroleum spirit. Its aqueous solution is coloured bluish
violet by ferric chloride ; if this solution be heated, white needles
of dehydro vanillin separate out. This body, which will be
described among the compounds containing two aromatic nuclei,
has the following constitution : 2

C C H 2 (OH)(OCH 3 )CHO
CyH 2 (OH)(OCH 3 )CHG'

Vanillin is reduced in dilute alcoholic solution by sodium
amalgam to vanillyl alcohol, C 6 H 3 (OH)(OCH 3 )CH 2 .OH, which
crystallizes in prisms, melting at 115 . 3

Vanillin has an acid reaction and forms salts, which have
been investigated by Carles, and by Tiemann and Haarmann ;
the former has also prepared bromine and iodine substitution
compounds.

2191 Isovanillin, C 6 H 3 (COH)(OH)(OCH 3 ) (1 : 3 : 4), is
formed by heating opianic acid, C 6 H 2 (COH)(OCH 3 ) 2 CO 2 H, to
160 170 with dilute hydrochloric acid; it crystallizes from hot
water in monosym metric prisms, which possess a vitreous lustre,
and its solution is not coloured by ferric chloride ; it sublimes
when heated, undergoing slight decomposition ; 4 its vapour has
a pleasant smell, resembling that of vanilla and anise.

Methylvanillin, or Dimdhylprotocatcchuicaldehydc, C r) H 3 (OCH.;).,
CHO, is formed by heating potassium vanillin with methyl
iodide and wood-spirit. 5 Beckett and Wright prepared it by
distilling opianic acid with soda lime. 6 It is slightly soluble in
hot water, readily in alcohol, and crystallizes in needles, which
smell like vanilla ; it melts at 42 43 and boils at 280 285.

Pcllotier, Ann. Clicm. Pharm. vi. 31 ; Sobrcro, ibid. liv. 67.

Tiemann, Her. Dcutsch. Chcm. Gcs. xviii. 3493.

Ibid. viii. 1125 ; ix. 415 ; xviii. 1597.

Wegscheklcr, Monatsch. Chcm. iii. 789.

Tiemann, Bcr. Dcutsch. Chcm. Ges. viii. 1135,

Journ. Chcm. Soc. 1876, i. 287.



VANILLIN COMPOUNDS. 317

Acdylwnillin, C 6 H 3 (OCO.CH 3 )(OCH 3 )CHO, is obtained by
the action of sodium vanillin on an ethereal solution of acetic
anhydride. It crystallizes in large, flat needles, melting at 77 . 1

Glucwanillin, or Vanillin glucoside, C 6 H^(OCH)(C)C 6 H 11 6 6 )
CHO + 2H 2 O, is formed by the oxidation of coniferin with a
dilute solution of chromic acid. It is tolerably soluble in water,
less readily in alcohol, and crystallizes from dilute alcohol in
white needles which lose their water at 100 and melt at 192. It
is readily decomposed by emulsin into grape sugar and vanillin,
and is converted by sodium amalgam and water into glucovanillyl
alcohol, C H 3 (OCH 3 )(OC 6 H n O 6 )CH 2 .OH + H 2 O, which crys-
tallizes in white needles, melting at 120. When its aqueous
solution is treated with a little emulsin and allowed to stand for
four or five days at 30 40, vanillyl alcohol is formed, and can
most easily be obtained pure by this method. 2

Piperonal, or Mcthyleneprotocateckuicaldchyde, C H 3 (O 2 CH 2 )
CHO, was prepared by Fittig and Mielk by the oxidation of
piperic acid, C c H 3 fO 2 CH 2 )C 4 H 4 .CO 2 H, with potassium per-
manganate. 3 It is slightly soluble in cold, more readily in hot
water and forms long, thin, lustrous plates, which have a very
pleasant smell, resembling that of the heliotrope ; 4 it is on this
account employed in perfumery. 5

Piperonal melts at 37, boils at 263 and forms a vapour which
has a specific gravity of 5'18. A very characteristic reaction of
this substance is that it decomposes into protocatechuicaldehydc
and finely divided carbon when it is heated to 200 with dilute
hydrochloric acid : 7

/CHO /CHO

C H 3 f 0\ rn = C H 3 f OH + C.
J



Oxidizing agents convert it into piperonylic acid, while sodium
amalgam reduces it in boiling aqueous solution to pipcronyl

1 Tiemann and Nagai, Bar. Dcutsch. Chcm. Gca. xi. 647.

2 Ticmann, ibid, xviii. 1595. s Ann. Chcm. rhnrm. clii. 35.

4 This same smell is possessed by " vanillon," a kind of vanilla, which forms
tliirk, fleshy capsules, and is obtained from the West Indies. It is only employed
in perfumery for (he preparation of essence of heliotrope ; it contains no piperonal,
but vanillin and an oil which is probably bcnzaldehyde. The perfumers in
preparing essence of heliotrope add a little of this oil to the extract of vanillon.
If a little be added to a solution of pure vanillin, both substances can be
recognized by their smell for some time, but after standing for months, the
mixture acquires the smell of heliotrope (Tiemann and Haarmann, Ber. Dcutsch.
Chcm. Gcs. ix. 1287.) 5 Chcm. Zcit. 1884, 173.

6 Knecht, Bo: Dcutsch. Chcm. Gcs. x. 1274.

7 Fittig and Rcmsen, Ann. Chcm. Pharm. clxviii. 97.



348 AROMATIC COMPOUNDS.

alcohol, C 6 H 3 (O 2 CH 2 )CH 2 .OH, which is slightly soluble in cold,
more readily in hot water, and forms long, colourless crystals,
melting at 5 1 . 1

Dichloropiperonal, C 6 H 3 (O 2 CC1 2 )COH. When one molecule
of piperonal is heated with three molecules of phosphorus
pentachloride, the compound C 6 H 3 (O 2 CC1 2 )CHC1 2 is formed.
It is an oily liquid, which is decomposed by water into hydro-
chloric acid and dichloropiperonal ; the latter crystallizes from
toluene in needles, which melt at 90 and undergo the following
decomposition when heated with water :

/CHO /CHO

C 6 H 3 f-0\ ppl + 2H 2 = C 6 H 3 ^OH + CO 2 + 2HC1.
\O/ C ' b 2 \OH

Protocatechuicaldehyde was first prepared according to this
method by Fittig and Remsen.

2192 $-Mdhylorthodihydroxybenzaldehyde, or (S-Mctamethoxy-
salicylaldehyde, C 6 H 3 (OH)(OCH 3 )CHO (CHO: OH: OCH 3 =
1 : 2 : 3), is formed together with vanillin by heating guaiacol
with caustic soda and chloroform. On distillation with steam it
passes over first as a liquid, which smells like salicylaldehyde,
boils at 264 265 in a current of carbon dioxide, stains the
skin yellow and forms a deep yellow solution in alkalis. Ferric
chloride added to an alcoholic solution produces a green coloura-
tion containing a shade of violet.' 2

Metadihydroxylenzaldehyde, or ft-Rcsorcylaldehyde, C 6 H 3 (OH). 2
CHO (CHO : HO : HO 1 : 2 : 4), is obtained, along with
resorcyldialdehyde, C 6 H 2 (OH) 9 (CHO) 2 , by heating resorcinol
with caustic soda and chloroform. 3 It crystallizes from water in
yellowish needles, which melt at 134 135; its solution is
coloured reddish brown by ferric chloride. It is an unstable
substance and gradually decomposes in moist air into a red
powder.

Orthomethoxyparahydroxylenzaldehyde, C 6 H 3 (OH)(OCH 3 )CHO
(CHO : OCH 3 : OH =r 1 : 2 : 4), is formed, together with the
following compound and two resorcyldialdehydes, by heating
methylresorcinol with caustic soda and chloroform. 4 It is readily
soluble in alcohol, slightly in water and benzene, and crystallizes

1 Fittig and Remsen, Ann. Chem. Pharm. clix. 138.

2 Tiemann and Koppe, Ber. Deutsch. Chem. Ges. xiv. 2020.

3 Tiemann and Lewy, ibid. x. 2212.

4 Tiemann and Parrisius, ibid. xiil. 2365.



PARAMETHOXYSALICYLALDEHYDE. 349

from the latter in lustrous plates melting at 153. Its aqueous
solution is coloured a faint violet by ferric chloride. The acetyl-
derivative, C 6 H 3 (OC,H 3 0)(OCH 3 )CHO, is formed by adding the
potassium compound to nn ethereal solution of acetic anhydride ;
it crystallizes in needles, melting at 86.

Paramdlioxysalicylaldehyde, (COH: OH: OCH 3 =zl: 2: 4),
may also be obtained by heating 7-resorcyldialdehyde with caustic
potash and methyl iodide. It is almost insoluble in water and
crystallizes in plates, which have a characteristic, pleasant,
aromatic odour, melt at 62 63 and are very readily volatile.
It forms an intensely yellow solution in alkalis ; ferric chloride
produces a deep reddish yellow colouration in an alcoholic
solution.

Melting-point.

Dimethyl-/3-resorcylaldehyde, needles 68 69.

Diethyl-/3-resorcylaldehyde, lustrous plates . . . 71 72.

Paradihydroxylenzaldehyde, or Gentisinaldehyde, (CHO : OH :
OHrrl : 2 : 5), has been prepared from quinol by the action of
chloroform and caustic soda. It is readily soluble in water and
alcohol, and crystallizes in flat, lustrous yellow needles, melting
at 99; its aqueous solution is coloured a transient bluish green
by ferric chloride and intensely yellow by alkalis. 1

Methylparadihydroocylenzaldehyde, or Metamethoxysalicylalde-
hyde, (CHO : OH : OCH 3 rzl : 3 : 5), has been obtained from
methylquinol. 2 It is a yellow oil which has an aromatic odour,
solidifies in a freezing mixture to a radiating mass and then melts
at 4 ; it boils at 247 248 in a current of carbon dioxide. It
stains the skin yellow, forms an intensely yellow solution in
alkalis and in alcoholic solution is coloured a permanent bluish
green by ferric chloride. Its acetyl-compound crystallizes in
needles, melting at 63.

Melting-
point.

Dimethylparadihydroxybenzaldehyde, fine needles . .51
Ethylparadihydroxybenzaldehyde, thick, yellow prisms. 51^5
Uiethylparadihydroxybenzaldehyde, small needles 3 . .60

1 Tiemann and Miiller, Ber. Deutsch. Chem. Ges. xiv. 1986.

- Ibid. 1990.

3 Hantzsch, Journ. Prakt. Chem. [2] xxii. 464.



350 AROMATIC COMPOUNDS.



/OH

DIHYDROXYBENZOIC ACIDS, C H 3 CO.OH

\OH.

2193 The numbers appended designate the positions of the
groups C0 2 H : OH : OH.



PROTOCATECHUIC ACID, OR ORTHODIHYDKOXYBENZOIC
ACID (1:3: 4).

In the year 1859, Hesse, by the action of bromine on an
aqueous solution of quinic acid, C 7 H 12 O 6 , obtained " carbohydro-
kinonic acid," C 7 H 6 O 4 , which decomposed into hydroquinone
and carbon dioxide on heating. 1 Two years later Strecker found
that an acid is formed by fusing piperic acid with potash, which
resembles catechuic acid so closely that he at first thought that
they were identical, but as he subsequently found less carbon in
the new compound he named it protocatechuic acid. 2 It decom-
poses on heating into carbon dioxide and catechol, and should
therefore be isomeric with Hesse's acid. All the other properties
of the two acids, however, agreed so completely that most
chemists assumed their identity, the more so as catechol had been
previously found among the decomposition products of carbo-
hydrokinonic acid. Fittig and Macalpine then proved decisively
that they are identical, and that the differences observed by
Hesse were due to some error. 3

Protocatechuic acid has been obtained from various carbon
compounds by fusion with caustic potash. Catechin or catechuic
acid, 4 the maclurin which occurs in fustic, 5 and the luteolin
obtained from woad also yield phloroglucinol, while many resins
give parahydroxybenzoic acid in addition 6 (p. 826).

Its synthetical formation from sulphanisic acid, 7 paracresol-

1 Ann. Clicm. Pharm. oxii. 52 ; cxxii. 221.

2 Ibid, cxviii. 280. Strecker supposed that catechu contained two homologous
acids, which he named deutero- and trito-catechuic acids ; but this view has not
been confirmed.

3 Ibid, clxviii. 111.

4 Kraut and Delden, ibid, cxxviii. 285 ; Malin, ibid, cxxxiv. 118.

5 Barth and Pfaundler, ibid, cxxvii. 357.

G Barth and Hlnsiwetz, ibid. cxxx. 346 ; cxxxiv. 277 ; cxxxix. 78.
7 Malin, ibid. clii. 109.



PROTOCATECHUIO ACID. 351



sulphonic acid, 1 bromanisic acid, iodoparahydroxybenzoic acid,
sulphoparahydroxybenzoic acid and sulphometahydroxybenzoic
acid, 2 is of theoretical interest.

It is best prepared from East Indian kino, which is obtained
by making incisions in the bark of Ptcrocarpus Marsupium ; the
sap flows out and dries to a dark red, transparent mass, which is
employed in medicine as an adhesive, and for many purposes as
a substitute for catechu. One part of the finely-powered kino is
then gradually brought into a well-stirred melt of three parts of
caustic soda kept at a low temperature. When the mass has
become coloured a light orange brown, it is dissolved in 20 parts
of water, and the solution acidified with sulphuric acid, and
allowed to stand for twenty- four hours. The filtrate is extracted
with ether, the latter evaporated and the residue repeatedly
crystallized from water. 3 The aqueous solution of the acid may
also be precipitated with lead acetate, the precipitate washed
and finally decomposed by sulphuretted hydrogen (Barth and
Hlasiwetz).

According to Eijkman, protocatechuic acid occurs in the fruit
of lllicium rcligiosum*

It crystallizes in monoclinic needles, containing one molecule of
water which is lost at 100, and melts at 194 ; 5 it dissolves in
5355 parts of water at 14 and in 3-537 parts at 75 80, 6
is very soluble in alcohol, less so in ether, and almost insoluble
in boiling benzene. Its aqueous solution is coloured an intense
bluish green by ferric chloride, the colour being changed to dark
red by the addition of sodium carbonate. The solutions of its
salts are coloured violet by ferrous sulphate. It reduces an
ammoniacal silver solution, but not Folding's solution ; on dry
distillation, or when heated to 830 350 with caustic soda, it
decomposes into carbon dioxide and catechol. When nitrogen
trioxide is passed into its ethereal solution, oxalic and dihydroxy-
liirtaric acids are formed (Part II. p. 266), together with smaller
quantities of dinitrophenol, picric acid, dinitrodihydroxyquinone
and nitroparahydroxybenzoic acid. 7

Protocatechuic acid is produced along with benzoic acid when
gum benzoin is fused with caustic potash; a compound of the

Barth, Ann. C'hcm. Phann. cliv. 364.
Ibid. clix. 232.
Stenhouse, ibid, clxxvii. 188.
Ber. Deutsch. Ckcm. Ges. xviii. Ref. 281.
Barth and Schmidt, ibid. xii. 1265.
Tiemann and Nagai, ibid. x. 211.
7 Gruber, ibid. xii. 514.



352 AROMATIC COMPOUNDS.

formula C 7 H 6 3 + C 7 H 6 O 4 + 2H 2 is formed, crystallizing in short
prisms, and the two acids cannot be separated by re-crystallization
or by fractional precipitation with lead acetate. On treatment
with bromine, however, the parahydroxybenzoic acid is converted
into tribromophenol, while the protocatechuic acid remains
unaltered (Earth and Hlasiwetz).

Barium protocatechuate, (C 6 H 3 (OH) 2 C0 2 ) 2 Ba -f 5H 2 0, forms
granular crystals ; when its solution is treated with concentrated
baryta water, the basic salt separates out in warty crystals, which,
after drying at 130, have the formula (C 6 H 3 (O 2 Ba)C0 2 ) 2 Ba. 1

Lead protocatechuate, (C H 3 (OH) 2 C0 2 )Pb + 2H 2 O. An amor-
phous precipitate of (C 6 H 3 (OPb.OH) 2 CO 2 ) 2 Pb is obtained by the
addition of lead acetate to an aqueous solution of the acid ; the
solution of this in dilute acetic acid deposits the normal salt in
small crystals.

Methyl protocatechuate, C 6 H 3 (OH) 2 CO 2 .CH 3 , crystallizes from
hot water in needles, which melt at 134'5; ferric chloride colours
its aqueous solution green. 2

2194 Vanillicacid, C 6 H 3 (OCH 3 )(OH)CO 2 H,(C0 2 H:OCH 3 :OH
~ 1 : 3 : 4), was first obtained by Tiemann by the oxidation of
coniferin with potassium permanganate; 3 it is also formed by
the action of air on finely divided, moist vanillin, 4 and has been
prepared by various other reactions, which will be described
below. It crystallizes in needles, melting at 207 , 5 and sublimes
without decomposition; it dissolves in 850 parts of water at 14,
and in 39 parts at 100, is very readily soluble in alcohol, but
somewhat less so in ether ; it is not coloured by ferric chloride,
and in the pure state is quite odourless. 6 On heating with caustic
soda and chloroform, vanillin is formed and only one aldehydo-
vanillic acid, 7 proving that the hydroxyl-group is in the para-
position, since both ortho- and para-compounds may be formed
in this reaction (p. 286).

Methyl vanillate, C 6 H 3 (OCH 3 )(OH)C0 2 .CH 3 , crystallizes from
dilute alcohol in lustrous needles, melts at 62 63, and boils
at 285 287 . 8

Vanillic acid glucoside, or Glucovanillic acid, (C 6 H 3 (OCH 3 )
OC 6 H U O 5 )CO 2 H + H 2 O, is formed, together with glucovanillin, 9

Earth, Ann. Ghem. Pharm. cxlii. 246.

P. Meyer, Ber. Deutsch. Ghem. Ges. xi. 129.

Ibid. viii. 509. 4 Ibid. viii. 1123.

Ibid. ix. 414. 6 Ibid. x. 60.

Tiemann and Mendelsohn, ibid. ix. 1278.

Matsmoto, ibid. xi. 128. 9 Tiemann, ibid, xviii. 1595.



ISOVANILLIC ACID. 353



by the action of potassium permanganate on coniferin, and
crystallizes from hot water in fine prisms, which lose their
water of crystallization at 100, and melt at 210 212.
It is decomposed by emulsin or by boiling with dilute acids
into grape sugar and vanillic acid. 1

Acctylvanillic acid, C 6 H 3 (OCH 3 )(OCO.CH 3 )CO 2 H, is formed
by heating vanillic acid with acetic anhydride, 2 and from
eugenol acetate, C 6 H 3 (OCH 3 )(OC 2 H 3 0)C 3 H 5> acetylferulic acid, 3
C 6 H 3 (OCH 3 )(OC 2 H 3 O)C 2 H. 2 .C0 2 H, acetylcreosol, 4 C C H 3 (OCH 8 )
(OC 2 H 3 0)CH 3 and acetylhomovauillic acid 5 by oxidation with
potassium permanganate. It crystallizes from dilute alcohol in
fine needles, which melt at 142, and are decomposed on boiling
with caustic potash into acetic and vanillic acids.

Benzmjlvanillic acid, C 6 H 3 (OCH 3 )(OCO.C H 6 )C0 2 H, is pre-
pared by the oxidation of benzoyl eugenol, and crystallizes from
dilute alcohol in small plates which have a peculiar surface
lustre, and melt at 178. 6

Isovanillic acid, C 6 H 3 (OH)(OCH 3 )CO 2 H, (C0 2 H : OH : OCH 3
~ 1 : 3 : 4). Tiemann found that when dimethylprotocatechuic
acid is heated with dilute hydrochloric acid, vauillic acid and
an isomeric methylprotocatechuic acid are formed, 7 the latter
being, as was proved by Beckett and Wright, 8 identical with
an acid which Matthiessen and Foster had previously ob-
tained by heating hemipinic acid, C 6 H 2 (OCH 3 ) 2 (COoH) 2 , with
hydrochloric acid. 9 According to Matsmoto, who proposed the
name isovanillic acid, it is most readily prepared by heating
2 parts of dimethylprotocatechuic acid to 160 170 with a
mixture of 25 parts of hydrochloric acid of specific gravity 1'2
and 50 parts of water for four to five hours. The product
is repeatedly crystallized from water in order to remove vanillic



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