Benzoic acid

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Benzoic acid
Skeletal formula Ball-and-stick model
Benzoic acid crystals
Benzoic acid crystals
Identifiers
CAS number 65-85-0 YesY
PubChem 243
ChemSpider 238 YesY
UNII 8SKN0B0MIM YesY
EC number 200-618-2
DrugBank DB03793
KEGG D00038 YesY
MeSH benzoic+acid
ChEBI CHEBI:30746 YesY
ChEMBL CHEMBL541 YesY
RTECS number DG0875000
Beilstein Reference 636131
Gmelin Reference 2946
3DMet B00053
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C7H6O2
Molar mass 122.12 g mol−1
Appearance Colorless crystalline solid
Odor faint, pleasant odor
Density 1.2659 g/cm3
Melting point 122.41 °C (252.34 °F; 395.56 K)[3]
Boiling point 249.2 °C (480.6 °F; 522.3 K)[1]
Solubility in water 2.9 g/L[1]
Solubility soluble in acetone, benzene, CCl4, chloroform, ethanol, ethyl ether, hexane, methanol, toluene
log P 1.87
Vapor pressure 0.001 hPa
Acidity (pKa) 4.202[2]
Refractive index (nD) 1.5397
Viscosity 1.26 mPa (130 °C)
Structure
Crystal structure Monoclinic
Molecular shape planar
Dipole moment 1.72 D in Dioxane
Thermochemistry
Specific
heat capacity
C
146.8 J/K mol
Std molar
entropy
So298
167.6 J/K mol
Std enthalpy of
formation
ΔfHo298
-385.2 kJ/mol
Hazards
MSDS JT Baker
EU Index Not listed
Main hazards Irritant
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 121.5 °C (250.7 °F; 394.6 K)[1]
Autoignition temperature 570 °C (1,058 °F; 843 K)[1]
LD50 1700 mg/kg (rat, oral)
Related compounds
Related carboxylic acids Hydroxybenzoic acids
Aminobenzoic acids,
Nitrobenzoic acids,
Phenylacetic acid
Related compounds Benzaldehyde,
Benzyl alcohol,
Benzoyl chloride,
Benzylamine,
Benzamide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Benzoic acid /bɛnˈz.ɪk/, C7H6O2 (or C6H5COOH), is a colorless crystalline solid and a simple aromatic carboxylic acid. The name is derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as food preservatives and benzoic acid is an important precursor for the synthesis of many other organic substances. The salts and esters of benzoic acid are known as benzoates /ˈbɛnz.t/.

History[edit]

Benzoic acid was discovered in the sixteenth century. The dry distillation of gum benzoin was first described by Nostradamus (1556), and then by Alexius Pedemontanus (1560) and Blaise de Vigenère (1596).[4]

Pioneer work in 1830 through a variety of experiences based on amygdalin, obtained from bitter almonds (the fruit of Prunus dulcis) oil by Pierre Robiquet and Antoine Boutron-Charlard, two French chemists, had produced benzaldehyde [5] but they failed in working out a proper interpretation of the structure of amygdalin that would account for it, and thus missed the identification of the benzoyl radical C7H5O. This last step was achieved some few months later (1832) by Justus von Liebig and Friedrich Wöhler, who determined the composition of benzoic acid.[6] These latter also investigated how hippuric acid is related to benzoic acid.

In 1875 Salkowski discovered the antifungal abilities of benzoic acid, which was used for a long time in the preservation of benzoate-containing cloudberry fruits.[7]

It is also one of the chemical compounds found in castoreum. This compound is gathered from the beaver plant food.[8]

Production[edit]

Industrial preparations[edit]

Benzoic acid is produced commercially by partial oxidation of toluene with oxygen. The process is catalyzed by cobalt or manganese naphthenates. The process uses cheap raw materials, and proceeds in high yield.[citation needed]

toluene oxidation

U.S. production capacity is estimated to be 126,000 tonnes per year (139,000 tons), much of which is consumed domestically to prepare other industrial chemicals.

Laboratory synthesis[edit]

Benzoic acid is cheap and readily available, so the laboratory synthesis of benzoic acid is mainly practiced for its pedagogical value. It is a common undergraduate preparation.

Benzoic acid can be purified by recrystallization from water because of its high solubility in hot water and poor solubility in cold water. The avoidance of organic solvents for the recrystallization makes this experiment particularly safe.[9] The solubility of benzoic acid in over 40 solvents with references to original sources can be found as part of the Open Notebook Science Challenge[10]

By hydrolysis[edit]

Like other nitriles and amides, benzonitrile and benzamide can be hydrolyzed to benzoic acid or its conjugate base in acid or basic conditions.

From benzaldehyde[edit]

The base-induced disproportionation of benzaldehyde, the Cannizzaro reaction, affords equal amounts of benzoate and benzyl alcohol; the latter can be removed by distillation.

Benzaldehyde Cannizzaro reaction.png

From bromobenzene[edit]

Bromobenzene can be converted to benzoic acid by "carbonation" of the intermediate phenylmagnesium bromide.[11] This synthesis offers a convenient exercise for students to carry out a Grignard reaction, an important class of carbon–carbon bond forming reaction in organic chemistry.[12][13]

C6H5Br + Mg(in dry ether) → C6H5MgBr
C6H5MgBr + CO2 → C6H5CO2MgBr
C6H5CO2MgBr + HCl → C6H5CO2H + MgBrCl

From benzyl alcohol[edit]

Benzyl alcohol is refluxed with potassium permanganate or other oxidizing reagents in water. The mixture is hot filtered to remove manganese dioxide and then allowed to cool to afford benzoic acid.

From benzyl chloride[edit]

Benzoic acid can be prepared by oxidation of benzyl chloride in the presence of alkaline KMnO4:

C6H5CH2Cl + 2 KOH + 2 [O] → C6H5COOH + KCl + H2O

Historical preparation[edit]

The first industrial process involved the reaction of benzotrichloride (trichloromethyl benzene) with calcium hydroxide in water, using iron or iron salts as catalyst. The resulting calcium benzoate is converted to benzoic acid with hydrochloric acid. The product contains significant amounts of chlorinated benzoic acid derivatives. For this reason, benzoic acid for human consumption was obtained by dry distillation of gum benzoin. Food-grade benzoic acid is now produced synthetically.

Uses[edit]

Benzoic acid is mainly consumed in the production of phenol by oxidative decarboxylation at 300−400 °C:[14]

C6H5CO2H + 1/2 O2 → C6H5OH + CO2

The temperature required can be lowered to 200 °C by the addition of catalytic amounts of copper(II) salts. The phenol can be converted to cyclohexanol, which is a starting material for nylon synthesis.

Precursor to plasticizers[edit]

Benzoate plasticizers, such as the glycol-, diethylenegylcol-, and triethyleneglycol esters, are obtained by transesterification of methyl benzoate with the corresponding diol. Alternatively these species arise by treatment of benzoylchloride with the diol. These plasticizers are used similarly to those derived from terephthalic acid ester.

Precursor to sodium benzoate and related preservatives[edit]

Benzoic acid and its salts are used as a food preservatives, represented by the E-numbers E210, E211, E212, and E213. Benzoic acid inhibits the growth of mold, yeast[15] and some bacteria. It is either added directly or created from reactions with its sodium, potassium, or calcium salt. The mechanism starts with the absorption of benzoic acid into the cell. If the intracellular pH changes to 5 or lower, the anaerobic fermentation of glucose through phosphofructokinase is decreased by 95%. The efficacy of benzoic acid and benzoate is thus dependent on the pH of the food.[16] Acidic food and beverage like fruit juice (citric acid), sparkling drinks (carbon dioxide), soft drinks (phosphoric acid), pickles (vinegar) or other acidified food are preserved with benzoic acid and benzoates.

Typical levels of use for benzoic acid as a preservative in food are between 0.05–0.1%. Foods in which benzoic acid may be used and maximum levels for its application are controlled by international food law.[17][18]

Concern has been expressed that benzoic acid and its salts may react with ascorbic acid (vitamin C) in some soft drinks, forming small quantities of benzene.[19]

Medicinal[edit]

Benzoic acid is a constituent of Whitfield's ointment which is used for the treatment of fungal skin diseases such as tinea, ringworm, and athlete's foot.[20][21] As the principal component of benzoin resin, benzoic acid is also a major ingredient in both tincture of benzoin and Friar's balsam. Such products have a long history of use as topical antiseptics and inhalant decongestants.

Benzoic acid was used as an expectorant, analgesic, and antiseptic in the early 20th century.[22]

Benzoyl chloride[edit]

Benzoic acid is a precursor to benzoyl chloride, C6H5C(O)Cl by treatment with thionyl chloride, phosgene or one of the chlorides of phosphorus. is an important starting material for several benzoic acid derivates like benzyl benzoate, which is used in artificial flavours and insect repellents.

Niche and laboratory uses[edit]

In teaching laboratories, benzoic acid is a common standard for calibrating a bomb calorimeter.[23]

Biology and health effects[edit]

Benzoic acid is relatively nontoxic. It is excreted as hippuric acid.[24]

Benzoic acid occurs naturally as do its esters in many plant and animal species. Appreciable amounts have been found in most berries (around 0.05%). Ripe fruits of several Vaccinium species (e.g., cranberry, V. vitis macrocarpon; bilberry, V. myrtillus) contain as much as 0.03–0.13% free benzoic acid. Benzoic acid is also formed in apples after infection with the fungus Nectria galligena. Among animals, benzoic acid has been identified primarily in omnivorous or phytophageous species, e.g., in viscera and muscles of the Rock Ptarmigan (Lagopus muta) as well as in gland secretions of male muskoxen (Ovibos moschatus) or Asian bull elephants (Elephas maximus).[25]

Gum benzoin contains up to 20% of benzoic acid and 40% benzoic acid esters.[26]

Cryptanaerobacter phenolicus is a bacterium species that produces benzoate from phenol via 4-hydroxybenzoate[27]

Benzoic acid is present as part of hippuric acid (N-benzoylglycine) in urine of mammals, especially herbivores (Gr. hippos = horse; ouron = urine). Humans produce about 0.44 g/L hippuric acid per day in their urine, and if the person is exposed to toluene or benzoic acid, it can rise above that level.[28]

For humans, the World Health Organization's International Programme on Chemical Safety (IPCS) suggests a provisional tolerable intake would be 5 mg/kg body weight per day.[25] Cats have a significantly lower tolerance against benzoic acid and its salts than rats and mice. Lethal dose for cats can be as low as 300 mg/kg body weight.[29] The oral LD50 for rats is 3040 mg/kg, for mice it is 1940–2263 mg/kg.[25]

In Taipei, Taiwan, a city health survey in 2010 found that 30% of dried and pickled food products had too much benzoic acid, which is known to affect the liver and kidney,[30] along with more serious issues like excessive cyclamate.

Reactions[edit]

Reactions of benzoic acid can occur at either the aromatic ring or at the carboxyl group:

Aromatic ring[edit]

benzoic acid aromatic ring reactions

Electrophilic aromatic substitution reaction will take place mainly in 3-position due to the electron-withdrawing carboxylic group; i.e. benzoic acid is meta directing.

The second substitution reaction (on the right) is slower because the first nitro group is deactivating.[31] Conversely, if an activating group (electron-donating) was introduced (e.g., alkyl), a second substitution reaction would occur more readily than the first and the disubstituted product might accumulate to a significant extent.

Carboxyl group[edit]

All the reactions mentioned for carboxylic acids are also possible for benzoic acid.

benzoic acid group reactions

References[edit]

  1. ^ a b c d Record in the GESTIS Substance Database from the IFA
  2. ^ Harris, Daniel (2010). Quantitative Chemical Analysis (8 ed.). New York: W. H. Freeman and Company. pp. AP12. ISBN 9781429254366. 
  3. ^ Melting point of benzoic acid
  4. ^ Neumüller O-A (1988). Römpps Chemie-Lexikon (6 ed.). Stuttgart: Frankh'sche Verlagshandlung. ISBN 3-440-04516-1. OCLC 50969944. 
  5. ^ Nouvelles expériences sur les amandes amères et sur l'huile volatile qu'elles fournissent Robiquet, Boutron-Charlard, Annales de chimie et de physique, 44 (1830), 352–382,
  6. ^ Liebig J, Wöhler F (1832). "Untersuchungen über das Radikal der Benzoesäure". Annalen der Chemie, 3 (3): 249–282. doi:10.1002/jlac.18320030302. 
  7. ^ Salkowski E (1875). Berl Klin Wochenschr 12: 297–298. 
  8. ^ The Beaver: Its Life and Impact. Dietland Muller-Schwarze, 2003, page 43 (book at google books)
  9. ^ D. D. Perrin; W. L. F. Armarego (1988). Purification of Laboratory Chemicals (3rd ed.). Pergamon Press. p. 94. ISBN 0-08-034715-0. 
  10. ^ solubility of benzoic acid in organic solvents
  11. ^ Donald L. Pavia (2004). Introduction to Organic Laboratory Techniques: A Small Scale Approach. Thomson Brooks/Cole. pp. 312–314. ISBN 0-534-40833-8. 
  12. ^ Shirley, D. A. (1954). "The Synthesis of Ketones from Acid Halides and Organometallic Compounds of Magnesium, Zinc, and Cadmium". Org. React. 8: 28–58. 
  13. ^ Huryn, D. M. (1991). "Carbanions of Alkali and Alkaline Earth Cations: (ii) Selectivity of Carbonyl Addition Reactions". In Trost, B. M.; Fleming, I.. Comprehensive Organic Synthesis, Volume 1: Additions to C—X π-Bonds, Part 1. Elsevier Science. pp. 49–75. ISBN 978-0-08-052349-1. 
  14. ^ Maki, Takao; Takeda, Kazuo (2000). "Benzoic Acid and Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a03_555. ISBN 3527306730. .
  15. ^ A D Warth (1 December 1991). "Mechanism of action of benzoic acid on Zygosaccharomyces bailii: effects on glycolytic metabolite levels, energy production, and intracellular pH". Appl Environ Microbiol. 1991 December 57 (12): 3410–4. PMC 183988. PMID 1785916. 
  16. ^ Pastrorova I, de Koster CG, Boom JJ (1997). "Analytic Study of Free and Ester Bound Benzoic and Cinnamic Acids of Gum Benzoin Resins by GC-MS HPLC-frit FAB-MS". Phytochem Anal 8 (2): 63–73. doi:10.1002/(SICI)1099-1565(199703)8:2<63::AID-PCA337>3.0.CO;2-Y. 
  17. ^ GSFA Online Food Additive Group Details: Benzoates (2006)
  18. ^ EUROPEAN PARLIAMENT AND COUNCIL DIRECTIVE No 95/2/EC of 20 February 1995 on food additives other than colours and sweeteners (Consleg-versions do not contain the latest changes in a law)
  19. ^ BfR article Indications of the possible formation of benzene from benzoic acid in foods, BfR Expert Opinion No. 013/2006, 1 December 2005
  20. ^ "Whitfield Ointment". 
  21. ^ Charles Owens Wilson; Ole Gisvold; John H. Block (2004). Wilson and Gisvold's Textbook of Organic Medicinal and Pharmaceutical. Lippincott Williams & Wilkins. p. 234. ISBN 0-7817-3481-9. 
  22. ^ Lillard, Benjamin (1919). Practical druggist and pharmaceutical review of reviews. 
  23. ^ Experiment 2: Using Bomb Calorimetry to Determine the Resonance Energy of Benzene
  24. ^ Cosmetic Ingredient Review Expert Panel Bindu Nair (2001). "Final Report on the Safety Assessment of Benzyl Alcohol, Benzoic Acid, and Sodium Benzoate". Int J Tox 20 (Suppl. 3): 23–50. doi:10.1080/10915810152630729. PMID 11766131. 
  25. ^ a b c "Concise International Chemical Assessment Document 26: BENZOIC ACID AND SODIUM BENZOATE". 
  26. ^ Tomokuni K, Ogata M (1972). "Direct Colorimetric Determination of Hippuric Acid in Urine". Clin Chem 18 (4): 349–351. PMID 5012256. 
  27. ^ Juteau, Pierre; Valérie Côté, Marie-France Duckett, Réjean Beaudet, François Lépine, Richard Villemur and Jean-Guy Bisaillon (January 2005). "Cryptanaerobacter phenolicus gen. nov., sp. nov., an anaerobe that transforms phenol into benzoate via 4-hydroxybenzoate". IJSEM 55 (1): 245–250. doi:10.1099/ijs.0.02914-0. PMID 15653882. 
  28. ^ Krebs HA, Wiggins D, Stubbs M (1983). "Studies on the mechanism of the antifungal action of benzoate". Biochem J 214 (3): 657–663. PMC 1152300. PMID 6226283. 
  29. ^ Bedford PG, Clarke EG (1972). "Experimental benzoic acid poisoning in the cat". Vet Rec 90 (3): 53–58. doi:10.1136/vr.90.3.53. PMID 4672555. 
  30. ^ Chen, Jian; Y.L. Kao (18 January 2010). "Nearly 30% dried, pickled foods fail safety inspections". The China Post. 
  31. ^ Brewster, R. Q.; Williams, B.; Phillips, R. (1955), "3,5-Dinitrobenzoic Acid", Org. Synth. ; Coll. Vol. 3: 337 

External links[edit]