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31-562: NHS is commonly found in organic chemistry or biochemistry where it is used as an activating reagent for carboxylic acids . Activated acids (carboxylates) can react with amines to form amides for example, whereas a normal carboxylic acid would just form a salt with an amine. A common way to synthesize an NHS-activated acid is to mix NHS with the desired carboxylic acid and a small amount of an organic base in an anhydrous solvent. A coupling reagent such as dicyclohexylcarbodiimide (DCC) or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)

62-401: A carboxylic acid is an organic acid that contains a carboxyl group ( −C(=O)−OH ) attached to an R-group . The general formula of a carboxylic acid is often written as R−COOH or R−CO 2 H , sometimes as R−C(O)OH with R referring to an organyl group (e.g., alkyl , alkenyl , aryl ), or hydrogen , or other groups. Carboxylic acids occur widely. Important examples include

93-777: A ligand in an inorganic or organometallic complex (a metal carbonyl , e.g. nickel carbonyl ). The remainder of this article concerns itself with the organic chemistry definition of carbonyl, such that carbon and oxygen share a double bond. In organic chemistry, a carbonyl group characterizes the following types of compounds: Other organic carbonyls are urea and the carbamates , the derivatives of acyl chlorides chloroformates and phosgene , carbonate esters , thioesters , lactones , lactams , hydroxamates , and isocyanates . Examples of inorganic carbonyl compounds are carbon dioxide and carbonyl sulfide . A special group of carbonyl compounds are dicarbonyl compounds, which can exhibit special properties. For organic compounds,

124-407: A of acetic acid is 4.76 whereas trifluoroacetic acid, with a trifluoromethyl substituent , has a p K a of 0.23). Electron-donating substituents give weaker acids (the p K a of formic acid is 3.75 whereas acetic acid, with a methyl substituent , has a p K a of 4.76) Deprotonation of carboxylic acids gives carboxylate anions; these are resonance stabilized , because the negative charge

155-437: A base and deprotonates the acid. A second equivalent will attack the carbonyl group to create a geminal alkoxide dianion, which is protonated upon workup to give the hydrate of a ketone. Because most ketone hydrates are unstable relative to their corresponding ketones, the equilibrium between the two is shifted heavily in favor of the ketone. For example, the equilibrium constant for the formation of acetone hydrate from acetone

186-428: A carboxylic acid, the carboxyl can be considered position one of the parent chain even if there are other substituents , such as 3-chloropropanoic acid . Alternately, it can be named as a "carboxy" or "carboxylic acid" substituent on another parent structure, such as 2-carboxyfuran . The carboxylate anion ( R−COO or R−CO − 2 ) of a carboxylic acid is usually named with the suffix -ate , in keeping with

217-426: A chlorine atom using thionyl chloride to give acyl chlorides . In nature, carboxylic acids are converted to thioesters . Thionyl chloride can be used to convert carboxylic acids to their corresponding acyl chlorides. First, carboxylic acid 1 attacks thionyl chloride, and chloride ion leaves. The resulting oxonium ion 2 is activated towards nucleophilic attack and has a good leaving group, setting it apart from

248-873: A large scale. They are also frequently found in nature. Esters of fatty acids are the main components of lipids and polyamides of aminocarboxylic acids are the main components of proteins . Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. Industrially important carboxylic acids include acetic acid (component of vinegar, precursor to solvents and coatings), acrylic and methacrylic acids (precursors to polymers, adhesives), adipic acid (polymers), citric acid (a flavor and preservative in food and beverages), ethylenediaminetetraacetic acid (chelating agent), fatty acids (coatings), maleic acid (polymers), propionic acid (food preservative), terephthalic acid (polymers). Important carboxylate salts are soaps. In general, industrial routes to carboxylic acids differ from those used on

279-531: A low solubility in water (0.2 g/L), but its sodium salt is very soluble in water. Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilized dimers through hydrogen bonds . For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporized, increasing the enthalpy of vaporization requirements significantly. Carboxylic acids are Brønsted–Lowry acids because they are proton (H ) donors. They are

310-523: A normal carboxylic acid. In the next step, 2 is attacked by chloride ion to give tetrahedral intermediate 3 , a chlorosulfite. The tetrahedral intermediate collapses with the loss of sulfur dioxide and chloride ion, giving protonated acyl chloride 4 . Chloride ion can remove the proton on the carbonyl group, giving the acyl chloride 5 with a loss of HCl . [REDACTED] Phosphorus(III) chloride (PCl 3 ) and phosphorus(V) chloride (PCl 5 ) will also convert carboxylic acids to acid chlorides, by

341-483: A sharp band associated with vibration of the C=O carbonyl bond ( ν C=O ) between 1680 and 1725 cm . A characteristic ν O–H band appears as a broad peak in the 2500 to 3000 cm region. By H NMR spectrometry, the hydroxyl hydrogen appears in the 10–13 ppm region, although it is often either broadened or not observed owing to exchange with traces of water. Many carboxylic acids are produced industrially on

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372-474: A similar mechanism. One equivalent of PCl 3 can react with three equivalents of acid, producing one equivalent of H 3 PO 3 , or phosphorus acid , in addition to the desired acid chloride. PCl 5 reacts with carboxylic acids in a 1:1 ratio, and produces phosphorus(V) oxychloride (POCl 3 ) and hydrogen chloride (HCl) as byproducts. Carboxylic acids react with Grignard reagents and organolithiums to form ketones. The first equivalent of nucleophile acts as

403-406: A smaller scale because they require specialized equipment. Preparative methods for small scale reactions for research or for production of fine chemicals often employ expensive consumable reagents. Many reactions produce carboxylic acids but are used only in specific cases or are mainly of academic interest. Carboxylic acids react with bases to form carboxylate salts, in which the hydrogen of

434-511: Is a highly chemoselective agent for carboxylic acid reduction. It selectively activates the carboxylic acid to give the carboxymethyleneammonium salt, which can be reduced by a mild reductant like lithium tris( t -butoxy)aluminum hydride to afford an aldehyde in a one pot procedure. This procedure is known to tolerate reactive carbonyl functionalities such as ketone as well as moderately reactive ester, olefin, nitrile, and halide moieties. The hydroxyl group on carboxylic acids may be replaced with

465-452: Is commercially available, and can be added to a protein to obtain a fluorescently labeled protein in a straightforward reaction and purification step). NHS can be used with EDC to immobilize enzymes for biosensor applications. Some alternatives to NHS are the water-soluble analog sulfo-NHS , hydroxybenzotriazole (HOBt), 1-hydroxy-7-azabenzotriazole (HOAt), and pentafluorophenol . Carboxylic acid In organic chemistry ,

496-533: Is delocalized over the two oxygen atoms, increasing the stability of the anion. Each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon's partial positive charge is also weakened by the - / 2 negative charges on the 2 oxygen atoms. Carboxylic acids often have strong sour odours. Esters of carboxylic acids tend to have fruity, pleasant odours, and many are used in perfume . Carboxylic acids are readily identified as such by infrared spectroscopy . They exhibit

527-400: Is only 0.002. The carboxylic group is the most acidic in organic compounds. The carboxyl radical , •COOH, only exists briefly. The acid dissociation constant of •COOH has been measured using electron paramagnetic resonance spectroscopy. The carboxyl group tends to dimerise to form oxalic acid . Carbonyl For organic chemistry , a carbonyl group is a functional group with

558-496: Is only useful for forming methyl esters. Like esters , most carboxylic acids can be reduced to alcohols by hydrogenation , or using hydride transferring agents such as lithium aluminium hydride . Strong alkyl transferring agents, such as organolithium compounds but not Grignard reagents , will reduce carboxylic acids to ketones along with transfer of the alkyl group. The Vilsmaier reagent ( N , N -Dimethyl(chloromethylene)ammonium chloride; [ClHC=N (CH 3 ) 2 ]Cl )

589-472: Is then added to form a highly reactive activated acid intermediate. NHS reacts to create a less labile activated acid. The group is usually written as SuO- or -OSu in chemical notation. Such an ester with acid and NHS, sometimes called succinate ester, is stable enough to be purified and stored at low temperatures in the absence of water and, as such, is commercially available. NHS esters are commonly used for protein modification (e.g. an NHS ester of fluorescein

620-464: The amino acids and fatty acids . Deprotonation of a carboxylic acid gives a carboxylate anion . Carboxylic acids are commonly identified by their trivial names . They often have the suffix -ic acid . IUPAC -recommended names also exist; in this system, carboxylic acids have an -oic acid suffix. For example, butyric acid ( CH 3 CH 2 CH 2 CO 2 H ) is butanoic acid by IUPAC guidelines. For nomenclature of complex molecules containing

651-552: The hydroxyl (–OH) group is replaced with a metal cation . For example, acetic acid found in vinegar reacts with sodium bicarbonate (baking soda) to form sodium acetate , carbon dioxide , and water: Widely practiced reactions convert carboxylic acids into esters , amides , carboxylate salts , acid chlorides , and alcohols . Their conversion to esters is widely used, e.g. in the production of polyesters . Likewise, carboxylic acids are converted into amides , but this conversion typically does not occur by direct reaction of

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682-422: The acidity of any adjacent C-H bonds. Due to the positive charge on carbon and the negative charge on oxygen, carbonyl groups are subject to additions and/or nucleophilic attacks. A variety of nucleophiles attack, breaking the carbon-oxygen double bond , and leading to addition-elimination reactions . Nucleophiliic reactivity is often proportional to the basicity of the nucleophile and as nucleophilicity increases,

713-402: The carbon-oxygen double bond . Interactions between carbonyl groups and other substituents were found in a study of collagen . Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond . Δ H σ values are much greater when the substituents on the carbonyl group are more electronegative than carbon. The polarity of C=O bond also enhances

744-422: The carboxylic acid and the amine. Instead esters are typical precursors to amides. The conversion of amino acids into peptides is a significant biochemical process that requires ATP . Converting a carboxylic acid to an amide is possible, but not straightforward. Instead of acting as a nucleophile, an amine will react as a base in the presence of a carboxylic acid to give the ammonium carboxylate salt. Heating

775-471: The formation of the anhydride via condensation is an equilibrium process. Under acid-catalyzed conditions, carboxylic acids will react with alcohols to form esters via the Fischer esterification reaction, which is also an equilibrium process. Alternatively, diazomethane can be used to convert an acid to an ester. While esterification reactions with diazomethane often give quantitative yields, diazomethane

806-418: The formula C=O , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes , ketones and carboxylic acids ), as part of many larger functional groups. A compound containing a carbonyl group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as

837-576: The general pattern of -ic acid and -ate for a conjugate acid and its conjugate base, respectively. For example, the conjugate base of acetic acid is acetate . Carbonic acid , which occurs in bicarbonate buffer systems in nature, is not generally classed as one of the carboxylic acids, despite that it has a moiety that looks like a COOH group. Carboxylic acids are polar . Because they are both hydrogen-bond acceptors (the carbonyl −C(=O)− ) and hydrogen-bond donors (the hydroxyl −OH ), they also participate in hydrogen bonding . Together,

868-593: The hydroxyl and carbonyl group form the functional group carboxyl. Carboxylic acids usually exist as dimers in nonpolar media due to their tendency to "self-associate". Smaller carboxylic acids (1 to 5 carbons) are soluble in water, whereas bigger carboxylic acids have limited solubility due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers and alcohols. Aqueous sodium hydroxide and carboxylic acids, even hydrophobic ones, react to yield water-soluble sodium salts. For example, enanthic acid has

899-453: The length of the C-O bond does not vary widely from 120 picometers . Inorganic carbonyls have shorter C-O distances: CO , 113; CO 2 , 116; and COCl 2 , 116 pm. The carbonyl carbon is typically electrophilic . A qualitative order of electrophilicity is RCHO (aldehydes) > R 2 CO (ketones) > RCO 2 R' (esters) > RCONH 2 (amides). A variety of nucleophiles attack, breaking

930-476: The most common type of organic acid . Carboxylic acids are typically weak acids , meaning that they only partially dissociate into [H 3 O] cations and R−CO − 2 anions in neutral aqueous solution. For example, at room temperature, in a 1- molar solution of acetic acid , only 0.001% of the acid are dissociated (i.e. 10 moles out of 1 mol). Electron-withdrawing substituents, such as -CF 3 group , give stronger acids (the p K

961-415: The salt to above 100 °C will drive off water and lead to the formation of the amide. This method of synthesizing amides is industrially important, and has laboratory applications as well. In the presence of a strong acid catalyst, carboxylic acids can condense to form acid anhydrides. The condensation produces water, however, which can hydrolyze the anhydride back to the starting carboxylic acids. Thus,

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