BENZOIC ACID. 



BENZOIC ACID. 



Benzoate of lime (CaO C 14 H 5 3 + 4HO) ia prepared by neutralising 

 benzoic acid with milk of lime, precipitating the slight excess of Hine 

 with carbonic acid, warming, filtering, and evaporating. Benzoate of 

 lime crystallises in needles or miclei, which dissolve in from 20 to 30 

 parts of cold water. On heating benzoate of lime, a part of the carbon 

 remains behind to form carbonate of lime, the rest is given off as 

 benzole, napthaline, and other hydrocarbons. 



Benzoate of baryta (BaOC l4 H,0 + 2HO), and Benzoate of strontia 

 (SrOC,,H s O H- 2HO) are very similar in their preparation and pro- 

 perties to the lime salt ; they are, however, less soluble than the latter 

 in cold water. They do not effloresce in the air. 



Bemoate of magnesia (MgOC 14 H 5 O s + ? HO), prepared like the salts of 

 the alkaline earths, is very soluble in water, and crystallises from its 

 solutions in well-defined efflorescent crystals. 



Benzoate of alumina is crystalline and soluble in water, but its 

 exact composition is not known. 



The benzoates of zinc, nickel, cobalt, and protoxide of iron are soluble 

 and crystallisable. The zinc salt is colourless, that of nickel green, 

 that of cobalt red, and that of protoxide of iron is nearly colourless, but 

 becomes green on exposure to the air. The peroxide of iron forms 

 several compounds with benzoic acid. The neutral benzoate of iron 

 dissolves partly in water, leaving a residue of a subsalt. An insoluble 

 benzoate of peroxide of iron is also formed by adding benzoate of 

 ammonia to a solution of chloride of iron nearly neutralised by 

 ammonia : the benzoate of iron so formed is said to have the com- 

 position, 2Fe,0 3 , 30,^,0, + 15HO. 



Benzoate of mamjanese (MnOC lt H 5 3 ) dissolves in 20 parts of cold, 

 and less of hot water; it crystallises from its solutions in transparent 

 needles. 



Benzoate of cadmium (CdO C lt H 5 3 + 2HO), prepared by saturating 

 hot aqueous solution of benzoic acid with carbonate of cadmium, 

 filtering and evaporating; crystallises in a mass of brilliant acicular 

 crystals. 



Benzoate of copper (CuOC 14 H,O s ). When sulphate of copper is 

 treated with a hot solution of benzoate of potash, a number of small light 

 bluish -gray needles of the benzoate of copper are precipitated, which, on 

 recrystallising from warm dilute acetic acid, are obtained as green 

 anhydrous crystals insoluble in alcohol. The products of the destruc- 

 tive distillation of benzoate of copper, are principally benzoic acid, 

 benzole, and benzoate of phenyL 



Mercury forms with benzoic acid two salts, corresponding to the 

 stages of oxidation of the mercury, Merruric benzoate (HgOC, 4 H 5 

 0, + HO) is precipitated as a white crystalline substance on adding 

 benzoate of potash to perchloride of mercury. It is very soluble 

 in hot, but insoluble in cold water. Mercurous benzoate (Hg^OC^HjO.,), 

 prepared similarly to the mercuric salt, resembles it in its appearance and 

 solubility in water. It is however turned yellow on exposure to the 

 light ; and on boiling, it is decomposed, metallic mercury being pre- 

 cipitated. 



Betizoate of silver (AgOC lt S t O,) is precipitated as a thick white 

 mass by bringing together soluble silver and benzoic salts. It is 

 almost insoluble in cold, but partially soluble in hot water, from 

 which solution it separates on cooling in the form of long crystalline 

 scales. 



Benznate of lead (PbOC 14 H a Oj + HO) is precipitated as a voluminous 

 crystalline powder, on mixing acetate of lead with benzoate of potash. 

 The water is driven off at about 212 Fahr., at which temperature the 

 salt melts. Benzoic acid also forms with lead other more basic com- 

 pounds, the constitution of which is little known. 



Benzoic acid combines also with the oxides of the organic radicals, 

 forming with them the corresponding benzoic ethers. The above- 

 described double anhydrous acids, namely, acetobenzoic and valero- 

 benzoic acid (C,H,0.,C 14 H S S and C.yH.O^.H.O.,), may be viewed as 

 benzoates of the oxides of the oxy-radicals, acetyl or othyl (C 4 H 3 0.j), and 

 valeryl (C.oH.0,). 



ate of methyl (C a H 3 C ,H 6 0,). To prepare this substance, two 

 parts by weight of benzoic acid are placed in a retort, and a mixture of 

 two parts of monohydrated sulphuric acid with one part of methylic 

 il is added, and the whole distilled until no more benzoate of 

 methyl appears in the distillate. Water is then added to the residue 

 in the retort, and the distillation repeated. It is advantageous that the 

 sulphuric acid and methylic alcohol should be mixed a day or two 

 beforehand, in order that methylosulphuric acid may have been fully 

 formed. The distillate is heated ill a water bath, to expel the uncom- 

 bined methylic alcohol, dried with chloride of calcium, and rectified 

 from oxide of lead, which retains any benzoic and sulphuric acids 

 which have been carried over mechanically, and sulphurous acid which 

 has been formed. Benzoate" of methyl is a transparent colourless 

 IT of pleasant odour, miscible with ether and alcohol, insoluble iu 

 water. Boiling-point 388 Fahr.; specific gravity, 1'087 at 60. Vapour 

 density, 4717. 



Benzoate of ethyl Benzoic ether (C 4 H 5 0, C 14 H 6 0,) is formed by 

 digesting for several hours, in a retort connected with an inverted and 

 well rooled condenser, four parts by weight of ethylic alcohol (89-90 

 per c.enl), two parts of benzoic acid, and one part of fuming hydro- 

 chloric acid. After the contents of the retort have stood a day, the 

 alcohol is distilled off from a water bath, and the benzoate of ethyl 

 precipitated by the addition of water to the residue in the retort. 



Another method is, to dissolve three parts of benzoic acid in two parts 

 of boiling alcohol, in a retort arranged as before, and to saturate ths 

 mixture with gaseous hydrochloric acid, and proceed as before. The 

 product from either mode of preparation is agitated with aqueous 

 carbonate of soda, washed with water, dried with chloride of calcium, 

 and rectified from oxide of lead. Benzoate of ethyl is transparent, 

 colourless, and of agreeable odour. Boiling-point, 415 Fahr.; specific 

 gravity, V055 at 50 ; vapour density, 5'406. Benzoate of ethyl, when 

 taken internally, has an intoxicating action, and is converted in the 

 system into hippuric acid, which appears in the urine. 



Benzoate of amyl (C 10 H n O, C 14 H 5 3 ) is prepared in the same manner 

 as the benzoate of ethyl, amylic alcohol being substituted for the 

 ethylic. It is a yellowish liquid, insoluble in water, but soluble 

 in ether and alcohol. Boiling-point, 502; specific gravity, 0'992 

 at 57. 



Benzoate of phenyl Benzophenide (C 15 H 5 0, C 14 H 5 0.,). When carbolic 

 acid is gently heated with chloride of benzoyl until hydrochloric acid 

 ceases to be evolved, the product on cooling solidifies to a crystalline 

 mass containing the benzoate of phenyL 



CuHeOj + C 14 H 5 O 2 C1 = C 18 H b OC, 4 H 5 O S + HC1. 



Catholic acid. Chloride of Benzoate of Phenyl. 

 Benzoyl. 



The compound is obtained pure by solution in a mixture of alcphol 

 and ether, and evaporation ; an insoluble oily body which is generally 

 formed, and which is probably a mixture of the .benzoate of phenyl 

 with some benzoate of ethyl, being mechanically separated. Befizoate 

 of phenyl possesses the odour of geraniums ; it crystallises in rhombs, 

 which melt at 158 Fahr. 



All these three organic benzoates are slowly converted by hydrate of 

 potash into benzoate of potash and the corresponding alcohols; and 

 this decomposition is effected more rapidly if alcoholic caustic potash 

 be employed. Anhydrous benzoic acid may also be made to combine 

 directly with the aldehydes, ethylic aldehyde and valeral, by sealing the 

 two together in glass tubes, and heating to 63. The compounds formed 

 have the composition C 4 H 4 2 , 2C, 4 H 5 O., and C 10 H 10 0.,, 2C,,H 5 3 . 



Benzoic acid unites directly with anhydrous sulphuric acid, forming 

 therewith a copulated acid, sulphobenzoic acid (C 14 H,,0 4 2S0 3 ) As this 

 acid, however, combines with two atoms of base to form neutral salts, 

 its formula is probably 2HO, C 14 H 4 2 2S0 3 . The acid is prepared by 

 leading the vapour of anhydrous sulphuric acid into benzoic acid as 

 long as heat is evolved. On treating the transparent mass so obtained 

 with water, and filtering, the free benzoic acid, being insoluble, is 

 separated. The filtrate is then saturated with carbonate of baryta and 

 filtered, whereby the free sulphuric acid remains behind as insoluble 

 sulphate. Enough hydrochloric acid is then added to the warm 

 filtrate to combine with half the barium present ; this converts the 

 soluble neutral sulphobenzoate into an insoluble acid, sulphobenzoate 

 of baryta, which separates out on cooling, and may be purified by 

 recrystallisation. The free acid is obtained from the acid baryta salt 

 by precipitating the baryta exactly with sulphuric acid, filtering and 

 evaporating, until a temperature of 300 Fahr. is reached. On cooling, 

 the sulphobenzoic acid separates out in the crystalline form. 



Of the sulphobenzoates, the bari/ta salts may be got by evaporating 

 the two solutions described in the above preparation of the free acid, 

 before and after the addition of the hydrochloric acid. The neutral 

 salt is anhydrous-(2BaOC 14 H 4 0. ! 2SO 3 ), and exceedingly stable. The 

 acid salt contains three atoms of water of crystallisation. The acid 

 and neutral potash salts are got from the corresponding baryta com- 

 pounds, by exact precipitation with sulphate of potash, and nitration. 

 The first is efflorescent, the second deliquescent, in the air. Neutral 

 sulphobenzoates of lead and silver are formed by digesting the free acid 

 with the corresponding metallic carbonates. The lead salt contains 

 four, the silver two, atoms of water. 



A tulphobenzoate of ethyl has been also formed by the action of 

 the chloride of sulphobenzoyl upon alcohol. Its properties have not 

 been much studied. 



By acting upon sulphobenzoic acid with pentachloride of phos- 

 phorus, a peculiar acid is obtained, which contains an atom of chlorine 



in place of one of hydrogen ; this is chlorobenzoic acid, [ HO, C^p.'Oj ]. 

 Its formation is preceded by that of the chloride of chlorbenzoyl 



(TT * 



Cjjpi'OjCl I, and it is prepared as follows : One part of sulpho- 

 benzoic acid is gently heated in a retort with two parts of peuta- 

 chloride of phosphorus. The heat is then carried to 338 Fahr., at 

 which temperature the oxychloride of phosphorus which has been 

 formed passes over. On changing the receiver, and applying a 

 stronger heat, sulphurous acid is disengaged, and the chloride of 

 chlorbenzoyl distils. On agitating this product with water, it is 

 decomposed into hydrochloric acid and chlorobenzoic acid. The latter 

 may be purified by combining it with potash, then boiling with caustic 

 potash, and precipitating by the addition of hydrochloric acid. Chloro- 

 benzoic acid is a colourless solid, which melts at 284' Fahr and readily 

 sublimes; it is soluble in ether, alcohol, and hot water, but insoluble 

 in cold water. Chlorobenzoic acid may also be formed by boiling 

 benzoic acid with chlorate of potash and hydrochloric acid. Fuming 



