2. Paracımmaric acit, ce parah, „trzzy-cinnamic acid, isomeric with coumarie weid, is octained by boling a solution of aices acutzlated with dite miştarie acid, and withdrawn from the filtered liquid by shaking with ether. It crystales in brittle Leedies. readily wible in not water and alcocoi, and meits at 179-190°. I unites with raveent hydrogen, forming hydro-paracoumaric aci (3 1693, 3), and gives acetate and paracay-benzoate on fusion WHA panasie tydrate.

Only one daydroxy-cinnamic acid is yet known.

(OH),

Caffeic acid, C ̧H ̧0,=CHCH CH.CO.OH

It is obtained from extract of coffee by boiling with potassie hydrate and addition A sulphuric acid; it forms yellowish prisms and plates scarcely soluble in cold water, more readily in hot water, and is very soluble in alcohol and ether. Ferric culoride gives a grass-green coloration, changing to red on addition of soda. On dry distillation it yields pyrocatechin amongst other products; fusion with potassic hydrate converts it into potassic acetate and protocatechuate:

CH(OH)CHCHCOOK + HOK + H,0 =H,
+ C,H,OH)z000K +CH 600k.

It unites with nascent hydrogen, forming hydrocaffeic acid. Caffetannic acid, a glucoside, accompanies caffeic acid in coffee extract; it can be precipitated from the alcoholic extract by plumbie acetate, and the resulting precipitate suspended in water and decomposed with sulphuretted hydrogen. The filtrate on evaporation yields a yellowish gummy mass of the acid. Its solutions are coloured green by ferric chloride, and on boiling with potassic hydrate split up into caffeic acid and an amorphous sugar-like substance. Its solution in lime water readily absorbs oxygen, becoming first a fine green, then blue, and finally brown.

1100. The following bodies also appear to belong to the cinnamic group:

12

Anethol, CHO, is contained in the oils of anise, fennel, star anise, &c., and crystallises out when the temperature is lowered. After pressing and recrystallisation from ether it forms colourless shining prisms, melting at 21° and boiling at 232°, sp. gr. 1·014. It unites with hydrochloric acid, forming a liquid compound:

Potassic hydrate at 200° decomposes anethol into para-oxybenzoic neid and anol, CH10. This latter is a phenol-like body, crystallising in white plates, melting at 92-5°. Boiling dilute nitric acid oxidises anethol to anisic aldehyde (§ 1033); chromic and sulphuric acids oxidise it to anisic acid (§ 1065). In both cases oxalic and carbonic neids are also formed. Concentrated sulphuric acid, phosphoric acid, zincic chloride, and iodine convert it into isomeric or polymeric modifications.

From these reactions the formula for anethol is probably :

CH.O.CH.C2H, (1:4),

in which, however, the constitution of the CH, group still remains uncertain.

1101. Eugenol, C10H1202, isomeric with cumic acid, is contained in the ethereal oils of Eugenia caryophyllata, Myrtus pimenta, Persea caryophyllata, and Canella alba, from which it can be extracted by shaking with potassic hydrate and obtained in a state of purity by precipitating the clear solution with carbonic anhydride. It is a colourless oil of aromatic odour; it boils at 253° and has sp. gr. 1.068 at 14°. The potassic compound has the formula C10HKO2; the baric compound, (C10H1102)2Ba, forms difficultly soluble nacreous plates. Treated with chlor-acetyl and chlor-benzoyl it gives acetyl and benzoyl derivatives. Benzoyl eugenol, C10H1102.C-H5O, forms colourless needles melting at 50°. Hydriodic acid decomposes eugenol into methylic iodide and a red resin, C,H1002:

H10H12O2 + HI = CH2I + C,H1002.

11

Fusion with potassic hydrate converts it into protocatechuic acid, acetic acid, carbonic anhydride, and hydrogen. From these reactions the formula

may be assigned to eugenol.

By the action of sodium and carbonic anhydride eugenol is converted into the sodic salt of eugetinic acid :

он

ONa

O.CH3

CH, O.CH3 + Na + CO2 = C6H2 CH2

CO.ONa

+ H2

from whose solution eugetinic acid is precipitated by hydrochloric acid. It forms colourless prisms, melts at 124°, and is difficultly soluble in water. At higher temperatures it again decomposes into carbonic anhydride and eugenol; with ferric chloride it gives a deep blue coloration.

C,H603

......

1102. Umbelliferone, C,н ̧ ̧ = CH ̧(OH) C2H2.CO

occurs

amongst the products of the dry distillation of galbanum and the resins from other umbelliferæ; it crystallises in rhombic prisms, melts at 240°, and dissolves with difficulty in water, the solution having a blue fluorescence. Treated with chlor-acetyl it gives a monacetate, CH¿(C2H ̧O)O3; with sodium amalgam and water, the sodic salt of umbellic acid (§ 1088).

1103. Homologues of Cinnamic Acid.-These bodies are all prepared by heating benzaldehyde or cumic aldehyde with an anhydride of an acid of the acetic series, the sodic salt of the same acid being present. The acids so far obtained are given below.

Phenyl crotonic acid, C10H10O2 = C6H5.C3H4.CO.OH, m.p. 78°.
Isophenyl crotonic acid, C10H1002, m.p. 83°-84°.

Phenyl angelic acid, CH12O2 = CH5.C1H.CO.Oн, m.p. 105°–

106°.

Cumenyl acrylic acid, C12H14O2 = C6H4(C3H7).C2H2.CO.OH, m.p. 157°-158°.

Cumenyl crotonic acid, C13H1602 = C6H1(C3H7).C2H1.CO.OH, m.p. 90°-91°.

Cumenyl angelic acid, C11H1O2 = C6H1(C ̧H7).С1H ̧.CO.OH,

m.p. 123°.

4

Phenyl Propicic Acid, C ̧H ̧0,

1104. Phenyl propiolie acid stands in the same relation to poenti propionie and eiLLanie acids as the acids of the CH-0, serves 14 854, to the fatty acids C„HO, and the members of the acryl acid series.

It is prepared synthetically by the action of sodium and carbonic anhydride on 3-brom-styrolene :

CH_Cr:CH + Nay + CO,=CH.C:CCOONa + NaBr + H and by the direct union of sodium phenyl acetylene (§ 1042) with carbonic anhydride:

C,H,C CNa+ CO2 = C2H2.C÷C.CO.ONa.

It is further obtained by heating a-brom-cinnamic acid with alcoholic potassic hydrate:

CH.C2HBr.CO.OK + KOH = KBr + H2O

It crystallises in colourless, volatile needles, melts between 136° and 137°, and is readily soluble in alcohol, ether, and hot water. Heated with water at 120° it splits up into carbonic anhydride and phenyl acetylene:

CH.CC.CO.OH = CO2 + C6H ̧.C÷CH.

It unites directly with four atoms of bromine, forming

CH.CBr.CBr2.CO.OH,

and with four atoms of nascent hydrogen yielding phenyl propionic acid. Chromic acid oxidises it to benzoic acid.

653

POLYBASIC AROMATIC ACIDS.

1105. The polybasic aromatic acids contain several acid groups, CO.OH, united to the benzene nucleus, either directly or by means of a hydrocarbon group. Their general properties, reactions, and methods of preparation correspond to those of the monobasic acids, but they unite more readily with nascent hydrogen with formation of additive products.

DIBASIC ACIDS.

Phenylene Dicarbonic Acids, C,H6O1 = C6H1(CO.OH)2.

1106. The three isomeric phenylene dicarbonic acids have already been referred to (§ 954) in reference to the aid afforded by them in determining the constitution of the isomeric disubstituted benzene derivatives. Their calcic salts all yield benzene when submitted to dry distillation with lime.

1107. Phthalic acid, or orthophenylene dicarbonic acid, (1:2), is formed by the oxidation of anthracene and many of its derivatives, also from several bodies derived from anthracene-such as alizarine and purpurine by oxidation with nitric acid, or manganic dioxide and sulphuric acid, and in small quantities by the action of the latter on benzene or benzoic acid. It crystallises in shining colourless tables or prisms, is readily soluble in hot water, alcohol, and ether, melts at 182°, and at higher temperatures decomposes into water and phthalic anhydride, which volatilise. On heating with hydriodic acid it yields carbonic anhydride and benzoic acid:

CH1(CO.OH)2 = CO2 + C6H5.CO.OH.

Benzoic acid is also obtained on heating two molecules of calcic phthalate with one molecule of lime at 330°-350°. Phthalic acid forms hydric and normal salts; they are crystalline and, with the exception of the alkali salts, difficultly soluble in water. The baric salt, CH (CO.O), Ba, crystallises in plates. Dimethylic and diethylic phthalates are obtained by saturation of solutions of the acid in the respective alcohols, are both colourless oily liquids which can be distilled.

=

.CO.

Phthalic anhydride, C,H,O, CH, COO, is formed directly by subliming phthalic acid, and also by treating phthalic acid with one molecule of phosphoric chloride (comp. § 835). It crystallises in long shining needles, melts at 127°-128°, and boils at 277°. It dissolves unaltered in alcohol and ether; in boiling water it is slowly converted

into phthalic acid. By action of two molecules of phosphoric chloride on phthalic acid

Phthalyl chloride, C2H ̧O2Cl2 = CH,(CO.Cl)2, is obtained as a yellow oil, boiling at 270°. On treatment with water it is slowly converted into hydrochloric and phthalic acids; with alcohols it yields ethereal phthalates, and with phenol it gives phenyl phthalate:

forming prisms melting at 61° and difficultly soluble in cold alcohol. Chlor phthalic acids are obtained by the oxidation of chlor-naphthalenes with dilute nitric acid. Dichlor-phthalic acid:

CH2Cl2(CO.OH)2,

prepared from dichlor-naphthalene tetrachloride, forms yellow prisms, melts at 183-185°, and is moderately soluble in water. Tetrachlor phthalic acid, CC,(CO.OH)2, obtained by oxidation of pentachlornaphthalene, crystallises in leaves and tables, and melts at 250°. On heating these acids decompose into water and chlor-anhydrides, in the latter case even on fusing.

On heating phthalic acid with nitro-sulphuric acid, nitro-phthalic acid, CH3(NO2)(CO.OH)2, is obtained in the form of yellow prisms, melting at 212° and moderately soluble in water; on treatment with tin and hydrochloric acid, carbonic anhydride is eliminated and metamido-benzoic acid formed.

1108. Hydrophthalic Acids.-Dihydrophthalic acid:

CH2O1 = C6H6(CƆ.OH)2,

is formed by the long-continued action of sodium amalgam on a cold solution of sodic phthalate, and is separated on addition of hydrochloric acid. It crystallises in plates and tables, is difficultly soluble in cold water and ether, readily in boiling water and alcohol. It fuses at 200° with decomposition into hydrogen, water, and phthalic anhydride. Its easy convertibility into benzoic acid and its derivatives is peculiar to it. This occurs on addition of bromine to an aqueous solution :

C&H (CO.OH)2 + Br2 = C6H5.CO.OH + CO2 + 2H Br,

or on oxidation with dilute nitric acid. Phosphoric chloride converts it into chlor-benzoyl and carbon monoxide:

=

CH(CO.OH)2 + 2PC1, C6H5.CO.Cl + CO + 2POCI2 + 3HCl. On saturating alcoholic solutions of the acid with hydrochloric acid the corresponding ethereal benzoates are formed.

Tetrahydrophthalic acid, C,H10O4 = CH,(CO.OH)2, is obtained by dry distillation of isohydropyromellitic acid, first as the anhydride, CH (CO),O, crystallising in plates and melting at 86°, which on treatment with water is converted into the acid. This crystallises in plates, melts at 96°, but already at this temperature decomposes into water and the anhydride. Hexahydrophthalic acid, C6H10(CO.OH)2, is obtained from both the preceding by heating at 230° with concentrated hydriodic acid, and also from tetrahydrophthalic acid by treatment with sodium amalgam. It melts at 207°, is difficultly soluble in water, and crystallises in plates or prisms.