Carboxylic acid 6099 223805333 2008-07-05T22:12:23Z Numbo3-bot 7118326 robot Adding: [[bn:কার্বক্সিলিক অ্যাসিড]] [[Image:Carboxylic-acid.svg|thumb|150px|Structure of a carboxylic acid]] [[Image:Carboxylic-acid-group-3D.png|thumb|150px|The 3D structure of the carboxyl group]] [[Image:Carboxyl-3D-space-filling-labelled.png|thumb|150px|A space-filling model of the carboxyl group]] '''Carboxylic acids''' are [[organic acid]]s characterized by the presence of a [[carboxyl group]], which has the [[Chemical formula|formula]] -C(=O)OH, usually written -COOH or -CO<sub>2</sub>H. <ref>[[Compendium of Chemical Terminology]], [http://goldbook.iupac.org/C00852.html carboxylic acids], accessed 15 Jan 2007.</ref> Carboxylic acids are [[Brønsted-Lowry acid-base theory|Brønsted-Lowry acids]] — they are proton donors. [[Salt]]s and [[anion]]s of carboxylic acids are called '''carboxylates'''. The simplest series of carboxylic acids are the '''alkanoic acids''', R-COOH, where R is a [[hydrogen]] or an [[alkyl]] [[Functional group|group]]. Compounds may also have two or more carboxylic acid groups per molecule. == Physical properties == [[Image:Carboxylic acid dimers.png|thumb|left|Carboxylic acid [[dimer]]s]] Carboxylic acids are [[polarity (chemistry)|polar]], and form [[hydrogen bond]]s with each other. At high temperatures, in vapor phase, carboxylic acids usually exist as dimeric pairs. Lower carboxylic acids (1 to 4 carbons) are miscible with water, whereas higher carboxylic acids are very much less-soluble due to the increasing hydrophobic nature of the alkyl chain. They tend to be rather soluble in less-polar solvents such as ethers and alcohols.<ref name=M&B>R.T. Morrison, R.N. Boyd. ''Organic Chemistry'', 6th Ed. (1992) ISBN 0-13-643669-2.</ref> Carboxylic acids are widespread in nature and are typically [[weak acid]]s, meaning that they only partially [[Dissociation (chemistry)|dissociate]] into H<sup>+</sup> [[cation]]s and RCOO<sup>−</sup> [[anion]]s in [[Water (molecule)|aqueous]] solution. For example, at room temperature, only 0.02&nbsp;% of all [[acetic acid]] molecules are dissociated in water. Since the carboxylic acids are weak acids, in water, both forms exist in an equilibrium: :RCOOH ↔ RCOO<sup>−</sup> + H<sup>+</sup> The acidity of carboxylic acids can be explained by either the stability of the acid or the stability of the [[conjugate base]] using [[inductive effect]]s or [[resonance (chemistry)|resonance]] effects. ===Stability of the acid=== Using inductive effects, the acidity of carboxylic acids can be rationalized by the two [[electronegative]] [[oxygen]] atoms distorting the electron clouds surrounding the O-H bond, weakening it. The weak O-H bond causes the acid molecule to be less stable, and causing the hydrogen atom to be labile, thus it dissociates easily to give the H<sup>+</sup> ion. Since the acid is unstable, the [[chemical equilibrium|equilibrium]] will lie on the right. Additional electronegative atoms or groups, such as chlorine or hydroxyl, substituted on the R-group have a similar, though lesser effect. The presence of these groups increases the acidity through [[inductive effects]]. For example, [[trichloroacetic acid]] (three -Cl groups) is a stronger acid than [[lactic acid]] (one -OH group), which in turn is stronger than acetic acid (no electronegative constituent). ===Stability of the conjugate base=== [[Image:Resonance stabilization of carboxylic acids.png|right|thumb|Resonance stabilization of carboxylic acids]] The acidity of a carboxylic acid can also be explained by [[resonance (chemistry)|resonance]] effects. The result of the dissociation of a carboxylic acid is a resonance stabilized product in which the negative charge is shared (delocalized) between the two oxygen atoms. Each of the carbon-oxygen bonds has what is called a partial double-bond characteristic. Since the conjugate base is stabilized, the above equilibrium lies on the right. ==Spectroscopy== Carboxylic acids are most readily identified as such by [[infrared spectroscopy]]. They exhibit a sharp C=O stretch between 1680 and 1725 cm<sup>−1</sup>, and the characteristic O-H stretch of the carboxyl group appears as a broad peak in the 2500 to 3000 cm<sup>−1</sup> region.<ref name=M&B/> In <sup>1</sup>H NMR spectrometry, the hydroxyl hydrogen appears in the 10-13 ppm region, though it is often either broadened or not observed due to exchange with any traces of water. ==Sources== Lower straight-chain [[aliphatic]] carboxylic acids, as well as those of even carbon number up to C<sub>18</sub>, are commercially available. For example, acetic acid is produced by [[methanol]] [[carbonylation]] with [[carbon monoxide]], whereas long chain carboxylic acids are obtained by the hydrolysis of [[triglyceride]]s obtained from plant or animal oils. Vinegar, a dilute solution of acetic acid, is biologically produced from the [[Fermentation (biochemistry)|fermentation]] of ethanol. It is used in food and beverages, but is not used in industry. == Synthesis == * Carboxylic acids can be produced by [[organic oxidation|oxidation]] of [[alcohol|primary alcohols]] and [[aldehyde]]s with strong oxidants such as [[Potassium Dichromate]], [[Jones reagent]], [[potassium permanganate]], or [[sodium chlorite]]. * They may also be produced by the oxidative cleavage of [[olefin]]s by [[ozonolysis]], [[potassium permanganate]], or [[potassium dichromate]]. In particular, any alkyl group on a benzene ring will be fully oxidized to a carboxylic acid, regardless of its chain length. This is the basis for the industrial synthesis of [[benzoic acid]] from [[toluene]]. *Carboxylic acids can also be obtained by the hydrolysis of [[nitrile]]s, [[ester]]s, or [[amide]]s, with the addition of acid or base. *They can also be prepared from the action of a [[Grignard reagent]] on [[carbon dioxide]], though this method is not used in industry. Carboxylic acids may also form from the following reactions: * Disproportionation of an [[aldehyde]] in the [[Cannizzaro reaction]] * Rearrangement of diketones in the [[benzilic acid rearrangement]] * Halogenation followed by hydrolysis of methyl ketones in the [[haloform reaction]] * Hydroformylation of an alkene followed by hydrolysis in the [[Koch reaction]] * Less-common reactions involving the generation of benzoic acids are the [[von Richter reaction]] from nitrobenzenes and the [[Kolbe-Schmitt reaction]] from [[phenol]]s. ==Reactions== *Carboxylic acids react with [[Base (chemistry)|bases]] to form carboxylate salts, in which the hydrogen of the hydroxyl (-OH) group is replaced with a metal [[cation]]. Thus, acetic acid found in vinegar reacts with [[sodium bicarbonate]] (baking soda) to form sodium acetate, [[carbon dioxide]], and water: :CH<sub>3</sub>COOH + NaHCO<sub>3</sub> → CH<sub>3</sub>COONa + CO<sub>2</sub> + H<sub>2</sub>O *Carboxylic acids also react with [[alcohol]]s and [[amine]]s to give [[ester]]s and [[amide]]s. Like other alcohols and [[phenol]]s, the hydroxyl group on carboxylic acids may be replaced with a chlorine atom using [[thionyl chloride]] to give [[acyl chloride]]s. *As with all carbonyl compounds, the protons on the [[alpha-carbon|α-carbon]] are labile due to keto-enol tautomerization. Thus the α-carbon is easily halogenated in the [[Hell-Volhard-Zelinsky halogenation]]. *The [[Arndt-Eistert synthesis]] inserts an α-methylene group into a carboxylic acid. *The [[Curtius rearrangement]] converts carboxylic acids to [[isocyanate]]s. *The [[Schmidt reaction]] converts carboxylic acids to [[amine]]s. *Carboxylic acids are decarboxylated in the [[Hunsdiecker reaction]]. * The [[Dakin-West reaction]] converts an amino acid to the corresponding amino ketone. * In the '''Barbier-Wieland degradation''' (1912), the alpha-methylene group in an aliphatic carboxylic acid is removed in a sequence of reaction steps, effectively a chain-shortening <ref>[[Organic Syntheses]], Coll. Vol. 3, p.234 (1955); Vol. 24, p.38 (1944) [http://www.orgsynth.org/orgsyn/pdfs/CV3P0234.pdf Link] </ref> <ref>[[Organic Syntheses]], Coll. Vol. 3, p.237 (1955); Vol. 24, p.41 (1944) [http://www.orgsynth.org/orgsyn/pdfs/CV3P0237.pdf Link].</ref>. * The addition of a carboxyl group to a compound is known as '''carboxylation'''; the removal of one is '''decarboxylation'''. [[Enzyme]]s that catalyze these reactions are known as [[carboxylase]]s ([[EC number|EC]] 6.4.1) and [[decarboxylase]]s (EC 4.1.1). == Nomenclature and examples == The [[carboxylate|carboxylate anion]] R-COO<sup>–</sup> is usually named with the suffix ''-ate'', so acetic acid, for example, becomes acetate ion. In [[IUPAC nomenclature]], carboxylic acids have an ''-oic acid'' suffix (e.g., octadecanoic acid). In [[common nomenclature]], the suffix is usually ''-ic acid'' (e.g., [[stearic acid]]). {|class = "wikitable" |+Straight-Chained, Saturated Carboxylic Acids !Carbon atoms !Common name !IUPAC name !Chemical formula !Common location or use |- |1 || [[Formic acid]] || Methanoic acid || HCOOH || Insect stings |- |2 || [[Acetic acid]] || Ethanoic acid || CH<sub>3</sub>COOH || [[Vinegar]] |- |3 || [[Propionic acid]] || Propanoic acid || CH<sub>3</sub>CH<sub>2</sub>COOH || |- |4 || [[Butyric acid]] || Butanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>COOH || Rancid butter |- |5 || [[Valeric acid]] || Pentanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>COOH || [[Valerian (herb)|Valerian]] |- |6 || Caproic acid || [[Hexanoic acid]] | CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>COOH || |- |7 || Enanthic acid || [[Heptanoic acid]] | CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>COOH || |- |8 || [[Caprylic acid]] || Octanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>COOH || Coconuts and breast milk |- |9 || Pelargonic acid || [[Nonanoic acid]] | CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>COOH || [[Pelargonium]] |- |10 || Capric acid || [[Decanoic acid]] | CH<sub>3</sub>(CH<sub>2</sub>)<sub>8</sub>COOH || |- |12 || [[Lauric acid]] || Dodecanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>10</sub>COOH || Coconut oil |- |16 || [[Palmitic acid]] || Hexadecanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>14</sub>COOH || Palm oil |- |18 || [[Stearic acid]] || Octadecanoic acid | CH<sub>3</sub>(CH<sub>2</sub>)<sub>16</sub>COOH || Some waxes, soaps, and oils |} Other carboxylic acids include: * Short-chain unsaturated monocarboxylic acids ** [[Acrylic acid]] (2-propenoic acid) – CH<sub>2</sub>=CHCOOH, used in polymer synthesis * [[Fatty acid]]s – medium to long-chain saturated and unsaturated monocarboxylic acids, with even number of carbons ** [[Docosahexaenoic acid]] – nutritional supplement ** [[Eicosapentaenoic acid]] – nutritional supplement * [[Amino acid]]s – the building blocks of [[protein]]s * [[Keto acids]] – acids of biochemical significance that contain a [[ketone]] group ** [[Pyruvic acid]] ** [[Acetoacetic acid]] * [[Aromatic compound|Aromatic]] carboxylic acids ** [[Benzoic acid]] – C<sub>6</sub>H<sub>5</sub>COOH; sodium benzoate, the sodium salt of benzoic acid is used as a food preservative ** [[Salicylic acid]] – found in many skin care products * [[Dicarboxylic acid]]s – containing two carboxyl groups ** [[Aldaric acid]] – a family of sugar acids ** [[Oxalic acid]] – found in many foods ** [[Malonic acid]] ** [[Malic acid]] – found in apples ** [[Succinic acid]] – a component of the [[citric acid cycle]] ** [[Glutaric acid]] ** [[Adipic acid]] – the monomer used to produce [[nylon]] * [[Tricarboxylic acid]]s – containing three carboxyl groups ** [[Citric acid]] – found in [[citrus fruit]]s ** [[Isocitric acid]] ** [[Aconitic acid]] ** [[Propane-1,2,3-tricarboxylic acid]] (tricarballylic acid, carballylic acid) * [[Alpha hydroxy acid]]s – containing a hydroxy group ** [[Lactic acid]] (2-hydroxypropanoic acid) – found in sour milk ==See also== {{Commonscat|Carboxylic acids}} * [[Acid anhydride]] * [[Acid chloride]] * [[Amide]] * [[Ester]] ==References== <div class="references-small"><references/></div> == External links == * Carboxylic acids pH and titration [http://www2.iq.usp.br/docente/gutz/Curtipot_.html - freeware for calculations, data analysis, simulation, and distribution diagram generation] {{Functional Groups}} [[Category:Carboxylic acids|*]] [[Category:Functional groups]] [[Category:Acids]] [[ar:حمض كربوكسيلي]] [[bn:কার্বক্সিলিক অ্যাসিড]] [[bs:Karboksilne kiseline]] [[bg:Карбоксилна киселина]] [[cs:Karboxylové kyseliny]] [[da:Carboxylsyre]] [[de:Carbonsäuren]] [[et:Karboksüülhapped]] [[es:Ácido carboxílico]] [[fa:کربوکسیلیک اسید]] [[fo:Carboxylsýra]] [[fr:Acide carboxylique]] [[ko:카복실산]] [[hr:Karboksilne kiseline]] [[id:Asam alkanoat]] [[it:Acidi carbossilici]] [[he:חומצה קרבוקסילית]] [[la:Acidum carboxylicum]] [[lv:Karbonskābes]] [[lt:Karboksirūgštys]] [[hu:Karbonsavak]] [[mk:Карбоксилна киселина]] [[ms:Asid karboksilik]] [[nl:Carbonzuur]] [[ja:カルボン酸]] [[no:Karboksylsyre]] [[nn:Karboksylsyre]] [[pl:Kwasy karboksylowe]] [[pt:Ácido carboxílico]] [[ro:Acid carboxilic]] [[ru:Карбоновые кислоты]] [[sk:Karboxylová kyselina]] [[sr:Карбоксилна киселина]] [[su:Asam karboksilat]] [[fi:Karboksyylihappo]] [[sv:Karboxylsyra]] [[th:กรดคาร์บอกซิลิก]] [[vi:Axít cacboxylic]] [[tr:Karboksilik asit]] [[uk:Карбонові кислоти]] [[zh:羧酸]]