Amine 1412 225880251 2008-07-15T20:54:58Z 71.101.33.94 it wont {{otheruses}} {{Redirect3|NH2|For the list of roads named National Highway 2, see [[National Highway 2]]}} [[Image:Amine-2D-general.png|thumb|150px|right|The general structure of an amine]] '''Amines''' are [[organic compound]]s and [[functional group]]s that contain a [[base (chemistry)|basic]] [[nitrogen]] [[atom]] with a [[lone pair]]. Amines are [[derivative (chemistry)|derivative]]s of [[ammonia]], wherein one or more [[hydrogen]] atoms are replaced by organic [[substituent]]s such as [[alkyl]] and [[aryl]] groups. Compounds with the nitrogen atom next to a [[carbonyl]] of the structure R-C(=O)NR<sub>2</sub> are called [[amide]]s and have different chemical properties. Important amines include [[amino acid]]s, [[biogenic amine]]s, [[trimethylamine]] (fish smell), and [[aniline]]; see [[:Category:Amines]] for a list of amines. ==Introduction== ===[[Aliphatic]] Amines=== As displayed in the images below, '''primary amines''' arise when one of three hydrogen atoms in ammonia is replaced by an organic substituent. '''Secondary amines''' have two organic substituents bound to N together with one H. In '''tertiary amines''' all three hydrogen atoms are replaced by organic substituents. It is also possible to have four alkyl substituents on the nitrogen. These compounds have a charged nitrogen center, and necessarily come with a negative counterion, so they are called quaternary [[ammonium]] salts. {| class="wikitable" style="margin: 1em auto 1em auto" ! Primary amine || Secondary amine || Tertiary amine |- | <center>[[Image:Primary-amine-2D-general.png|100px|primary amine]]</center> || <center>[[Image:Secondary-amine-2D-general.png|100px|secondary amine]]</center> || <center>[[Image:Amine-2D-general.png|100px|tertiary amine]]</center> |} Similarly, an organic compound with multiple amino groups is called a '''diamine''', '''triamine''', '''tetraamine''' and so forth. ===Aromatic amines=== {{main|Aromatic amines}} Aromatic amines have the nitrogen atom connected to an [[aromatic]] ring as in [[aniline]]s. The aromatic ring strongly decreases the [[base (chemistry)|alkalinity]] of the amine, depending on its substituents. Interestingly, the presence of an amine group strongly increases the reactivity of the aromatic ring, due to an electron-donating effect. One [[organic reaction]] involving aromatic amines is the [[Goldberg reaction]]. ==Naming conventions== * the prefix "N-" shows substitution on the nitrogen atom * as prefix: "amino-" * as suffix: "-amine" * remember that chemical compounds are not proper nouns, so lower case is indicated throughout. Systematic names for some common amines: {| border="0" align="center" spacing="5" |- valign="top" align="center" | Lower amines are named with the suffix ''-amine''.<br /> [[Image:methylamine.png|100px]]<br /> '''methylamine''' | Higher amines have the prefix ''amino'' as a functional group.<br /> [[Image:2-amino-pentane.png|150px]]<br /> '''2-aminopentane'''<br/>(or sometimes: ''pent-2-yl-amine'' or ''pentane-2-amine'') |} *'''Primary amines''': ** [[methylamine]] ** [[ethanolamine]] or 2-aminoethanol ** [[trisamine]] (or more commonly [[tris]]) (Its [[HCl]] salt is used as a [[pH]] [[buffering agent]] in [[biochemistry]]) *'''Secondary amines''': ** [[dimethylamine]] ** [[methylethanolamine]] or 2-(methylamino)ethanol ** [[Cyclic compound|Cyclic]] amines: *** [[aziridine]] (3-member ring), *** [[azetidine]] (4-member ring), *** [[pyrrolidine]] (5-member ring) and *** [[piperidine]] (6-member ring) *'''Tertiary amines''': ** [[trimethylamine]] ** [[dimethylethanolamine]] (DMEA) or 2-(dimethylamino)ethanol ** [[bis-tris]] (It is used as a pH buffering agent in biochemistry) ==Physical properties== ===General properties=== # [[Hydrogen bonding]] significantly influences the properties of primary and secondary amines as well as the protonated derivatives of all amines. Thus the [[boiling point]] of amines is higher than those of the corresponding [[phosphine]]s, but generally lower than those of the corresponding [[alcohol]]s. Alcohols, or alkanols, resemble amines but feature an -OH group in place of NR<sub>2</sub>. Since oxygen is more [[electronegative]] than nitrogen, RO-''H'' is typically more acidic than the related R<sub>2</sub>N-''H'' compound. # Methyl-, dimethyl-, trimethyl-, and [[ethylamine]] are gases under standard conditions, whereas [[diethylamine]] and [[triethylamine]] are liquids. Most other common alkyl amines are liquids; high-[[molecular-weight]] amines are, of course, solids. # Gaseous amines possess a characteristic ammonia smell, liquid amines have a distinctive "fishy" smell. # Most aliphatic amines display some solubility in water, reflecting their ability to form hydrogen bonds. Solubility decreases with the increase in the number of carbon atoms, especially when the carbon atom number is greater than 6. # Aliphatic amines display significant solubility in organic [[solvent]]s, especially polar organic solvents. Primary amines react with [[ketone]]s such as [[acetone]], and most amines are incompatible with [[chloroform]] and [[carbon tetrachloride]]. # The aromatic amines, such as [[aniline]], have their lone pair electrons [[conjugated system|conjugated]] into the benzene ring, thus their tendency to engage in hydrogen bonding is diminished. Otherwise they display the following properties: #* Their boiling points are usually still high <!--"higher": than what?-->due to their larger size. #* Diminished solubility in water, although they retain their solubility in suitable organic solvents only. #* They are toxic <!-- which one has: b.p.184 C?--> and are easily absorbed through the skin: thus hazardous. [[Image:Inversion_of_Amine.PNG|200px|right|amine inversion]] === Chirality=== Tertiary amines of the type NHRR' and NRR'R" are [[chirality (chemistry)|chiral]]: the nitrogen atom bears four distinct substituents counting the lone pair. The energy barrier for the [[nitrogen inversion|inversion]] of the stereocenter is relatively low, e.g., ~7 kcal/mol for a trialkylamine. The interconversion of the stereoisomers has been compared to the inversion of an open umbrella in to a strong wind. Because of this low barrier, amines such as NHRR' cannot be resolved optically and NRR'R" can only be resolved when the R, R', and R" groups are constrained in cyclic structures such as [[aziridines]]. Quaternary ammonium salts with four distinct groups on the nitrogen are capable of exhibiting optical activity. ===Properties as bases=== Like ammonia, amines act as [[base (chemistry)|bases]] and are reasonably strong (see table for examples of [[conjugate acid]] K<sub>a</sub> values). The basicity of amines depends on: #The electronic properties of the substituents (alkyl groups enhance the basicity, aryl groups diminish it). #[[Steric hindrance]] offered by the groups on nitrogen. #The degree of solvation of the protonated amine. The nitrogen atom features a [[lone electron pair]] that can bind H<sup>+</sup> to form an [[ammonium ion]] R<sub>3</sub>NH<sup>+</sup>. The lone electron pair is represented in this article by a two dots above or next to the N. The water [[solubility]] of simple amines is largely due to [[hydrogen bonding]] between protons on the water molecules and these lone electron pairs. * [[Inductive effect]] of alkyl groups {| class="toccolours" style="float: center; border-collapse: collapse; margin: 0em 1em;" border="1" cellpadding="2" cellspacing="0" ! Ions of compound ! K<sub>b</sub> |- | [[Ammonia]] NH<sub>3</sub> | 1.8·10<sup>-5</sup> M |- | [[Methylamine]] CH<sub>3</sub>NH<sub>2</sub> | 4.4·10<sup>-4</sup> M |- | [[propylamine]] CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub> | 4.7·10<sup>-4</sup> M |- | [[2-propylamine]] (CH<sub>3</sub>)<sub>2</sub>CHNH<sub>2</sub> | 5.3·10<sup>-4</sup> M |- | [[dimethylamine]] (CH<sub>3</sub>)<sub>2</sub>NH | 5.4·10<sup>-4</sup> M |- | [[trimethylamine]] (CH<sub>3</sub>)<sub>3</sub>N | 5.9·10<sup>-5</sup> M |- : +I effect of alkyl groups raises the energy of the lone pair of electrons, thus elevating the basicity. Thus the basicity of an amine may be expected to increase with the number of alkyl groups on the amine. However, there is no strict trend in this regard, as basicity is also governed by other factors mentioned above. Consider the Kb values of the methyl amines given above. The increase in Kb from methylamine to dimethylamine may be attributed to +I effect; however, there is a decrease from dimethylamine to trimethyl amine due to the predominance of steric hindrance offered by the three methyl groups to the approaching [[Lewis acid]]. * [[Mesomeric effect]] of aromatic systems {| class="toccolours" style="float: center; border-collapse: collapse; margin: 0em 1em;" border="1" cellpadding="2" cellspacing="0" ! Ions of compound ! K<sub>b</sub> |- | [[Ammonia]] NH<sub>3</sub> | 1.8·10<sup>-5</sup> M |- | [[Aniline]] C<sub>6</sub>H<sub>5</sub>NH<sub>2</sub> | 3.8·10<sup>-10</sup> M |- | [[4-methylphenylamine]] 4-CH<sub>3</sub>C<sub>6</sub>H<sub>4</sub>NH<sub>2</sub> | 1.2·10<sup>-9</sup> M |- | [[2-nitrophenylamine]] | 1.5·10<sup>-15</sup> M |- | [[3-nitrophenylamine]] | 2.8·10<sup>-13</sup> M |- | [[4-nitrophenylamine]] | 9.5·10<sup>-14</sup> M |- : -M effect of aromatic ring delocalises the lone pair of electrons on nitrogen into the ring, resulting in decreased basicity. Substituents on the aromatic ring, and their positions relative to the amine group may also considerably alter basicity as seen above. *The degree of solvation of protonated amines: {| class="toccolours" style="float: center; border-collapse: collapse; margin: 0em 1em;" border="1" cellpadding="2" cellspacing="0" ! Ions of compound ! Maximum number of H-bond |- | NH<sub>4</sub><sup>+</sup> | 4 Very Soluble in H<sub>2</sub>O |- | RNH<sub>3</sub><sup>+</sup> | 3 |- | R<sub>2</sub>NH<sub>2</sub><sup>+</sup> | 2 |- | R<sub>3</sub>NH<sup>+</sup> | 1 Least Soluble in H<sub>2</sub>O |- The degree of solvation of the protonated amine depends on the approachability of solvent molecules. If the molecule is sterically hindered (as in the case of trimethylamine), the protonated form is not well-solvated, thereby reducing basicity. This also explains the order of basicity of the methyl amines (see above). In the case of aprotic polar solvents (like [[DMSO]] and [[DMF]]), wherein the extent of solvation is not as high as in protic polar solvents (like water and methanol), the basicity of amines is almost solely governed by the electronic factors within the molecule. <!-- the following statement is incorrect or excessively vague: "Protonated ammonia is heavily solvated, making the cation most stable."--> == Synthesis ==<!-- This section is linked from [[Organic reaction]] --> The following laboratory methods exist for the preparation of amines: * via the [[Gabriel synthesis]]: [[Image:Gabriel Synthesis Scheme.png|500px|center|The Gabriel synthesis]] * via [[azide]]s by the [[Staudinger reduction]]. * From [[carboxylic acid]]s in the [[Schmidt reaction]]. * [[Allyl]]ic amines can be prepared from [[imine]]s in the [[Aza-Baylis-Hillman reaction]]. * via [[Hofmann rearrangement|Hofmann degradation]] of amides. This reaction is valid for preparation of primary amines only. Gives good yields of primary amines uncontaminated with other amines. [[Image:Hofmann Rearrangement Scheme.png|center|400px|The Hofmann rearrangment]] * [[Quaternary ammonium salt]]s upon treatment with strong base undergo the so-called [[Hofmann Elimination]] * [[Redox|Reduction]] of [[nitrile]]s, [[amide]]s and [[nitro compound]]s: [[Image:Nitrile_reduction.png|center|350px|Nitrile reduction]] :[[Nitrile]]s are reduced to amines using hydrogen in the presence of a nickel catalyst, although acidic or alkaline conditions should be avoided to avoid hydrolysis of -CN group. LiAlH<sub>4</sub> is more commonly employed for the reduction of nitriles on the laboratory scale. Similarly, LiAlH<sub>4</sub> reduces amides to amines: [[Image:Reduction-of-amide.gif|center|Reduction of amides to amines]] : The reduction of nitro compounds to amines can be accomplished with elemental [[zinc]], [[tin]] or [[iron]] with an [[acid]]. {{details|Reduction of nitro compounds}} * Nucleophilic substitution of haloalkanes <ref>For an example see: [[Org. Synth.]] '''2008''', 85, 10-14 [http://www.orgsynth.org/orgsyn/pdfs/V85P0010.pdf Article]</ref>. Primary amines can also be synthesized by alkylaton of ammonia. [[halogenoalkane|Haloalkanes]] react with amines to give a corresponding alkyl-substituted amine, with the release of a halogen acid. Such reactions, which are most useful for alkyl iodides and bromides, are rarely employed because the degree of alkylation is difficult to control. If the reacting amine is tertiary, a [[quaternary ammonium cation]] results in the [[Menshutkin reaction]]. Many [[quaternary ammonium salt]]s can be prepared by this route with diverse R groups and many halide and pseudohalide anions. [[Image:Alkylation_of_Amine.PNG|center|Amine alkylation]] [[Image:Formation_of_Quat.PNG|center|Amine alkylation]] * via halides and hexamine in the [[Delepine reaction]] * aryl amines can be obtained from amines and aryl halides in the [[Buchwald-Hartwig reaction]] * from alkenes and alkynes in [[hydroamination]] * from rearrangement of haloamines in the [[Hofmann-Löffler reaction]] * via amination of an alcohol with ammonia over a hydrogenating catalyst such as a nickel/copper alloy.<ref>http://www.freepatentsonline.com/4014933.html,"Production of Amines from Alcohols"</ref> == Reactions ==<!-- This section is linked from [[Organic reaction]] --> Amines react in a variety of ways: * By [[nucleophilic acyl substitution]]. [[Acyl chloride]]s and [[acid anhydride]]s react with primary and secondary amines in cold to form [[amide]]s in the [[Schotten-Baumann reaction]]. Tertiary amines cannot be acylated due to the absence of a replaceable hydrogen atom. With the much less active [[benzoyl chloride]], [[acylation]] can still be performed by the use of excess aqeous alkali to facilitate the reaction. [[Image:Amide_formation_from_amine.gif|center|Amide formation]] :Because amines are basic, they neutralize [[carboxylic acid]]s to form the corresponding ammonium carboxylate salts. Upon heating to 200&nbsp;°C, the primary and secondary amine salts dehydrate to form the corresponding [[amide]]s. [[Image:Amine_plus_Carboxylic_Acid.PNG|center|Amine reaction with carboxylic acids]] * By ammonium salt formation. Amines R<sub>3</sub>N react with strong acids such as [[hydroiodic acid]], [[hydrobromic acid]] and [[hydrochloric acid]] in neutralization reactions forming [[ammonium salt]]s R<sub>3</sub>NH<sup>+</sup>. * By [[diazonium salt]] formation. [[Nitrous acid]] with formula HNO<sub>2</sub> is unstable, therefore usually a mixture of NaNO<sub>2</sub> and dilute [[hydrochloric acid]] or [[sulfuric acid]] is used to produce nitrous acid indirectly. Primary aliphatic amines with nitrous acid give very unstable diazonium salts which spontaneously decompose by losing N<sub>2</sub> to form carbonium ion. The carbonium ion goes on to produce a mixture of [[alkene]]s, alkanols or [[alkyl halide]]s, with [[alkanol]]s as the major product. This reaction is of little synthetic importance because the diazonium salt formed is too unstable, even at cold conditions. : NaNO<sub>2</sub> + HCl → HNO<sub>2</sub> + NaCl [[Image:Nitrous_acid_with_n-amine.gif|center|Nitrous acid reaction]] :Primary aromatic amines, such as [[aniline]] (phenylamine) form more stable [[diazonium]] ions at 0&ndash;5&nbsp;°C. Above 5&nbsp;°C, they will decompose to give [[phenol]] and N<sub>2</sub>. Arenediazonium salts can be isolated in the crystalline form but are usually used in solution immediately after preparation, due to rapid decomposition on standing even when cold. The solid arenediazonium salt is explosive upon shock or mild warming. Because of their greater stability, arenediazonium salts are more synthetically useful than their aliphatic counterparts. Since it is not necessary to isolate the diazonium salt, once it is formed another reagent such as [[cuprous cyanide]] can simply be added to the mixture, and with gentle heating of the solution, a replacement reaction takes place along with the evolution of nitrogen. In addition, arenediazonium ions can also undergo a coupling reaction with a highly activated aromatic compound such as a [[phenol]] to form an [[azo compound]]. [[Image:Aromatic_diazonium_salt.gif|center|Aromatic diazonium salts]] * By [[Alkylimino-de-oxo-bisubstitution|imine formation]]. Primary amines react with [[ketone]]s and [[aldehyde]]s to form [[imine]]s. In the case of [[formaldehyde]] (R' = H), these products are typically cyclic [[trimer]]s. : RNH<sub>2</sub> + R'<sub>2</sub>C=O → R'<sub>2</sub>C=NR + H<sub>2</sub>O :Secondary amines react with ketones and aldehydes to form [[enamine]]s : R<sub>2</sub>NH + R'(R"CH<sub>2</sub>)C=O → R"CH=C(NR<sub>2</sub>)R' + H<sub>2</sub>O * By [[organic oxidation|oxidation]] to [[nitroso]] compounds, for instance with [[peroxymonosulfuric acid]]. * By reduction of [[quaternary ammonium cation]]s to tertiary amines in the [[Emde degradation]]. * By rearrangement of N-alkyl anilines to aryl substituted anilines in the [[Hofmann-Martius rearrangement]]. * primary and secondary amines react with pyridinium salts in the [[Zincke reaction]] * By cleavage (tertiary amines only) with cyanogen bromide in the [[Von Braun reaction]]. == Biological activity == Amines have strong, characteristic odors, and are toxic. The smells of ammonia, old fish, urine, rotting flesh, and semen are all mainly composed of amines. Many kinds of biological activity produce amines by breakdown of [[amino acid]]s. == Use of amines== === [[Dye]]s === Primary aromatic amines are used as a starting material for the manufacture of [[azo dye]]s. It reacts with nitric(III) acid to form diazonium salt, which can undergo coupling reaction to form azo compound. As azo-compounds are highly coloured, they are widely used in dyeing industries, such as: * [[Methyl orange]] * [[Direct brown 138]] * [[Sunset yellow]] FCF * [[Ponceau]] ===Drugs=== * [[Chlorpheniramine]] is an antihistamine that helps to relieve allergic disorders due to cold, hay fever, itchy skin, insect bites and stings. * [[Chlorpromazine]] is a tranquillizer that sedates without inducing sleep. It is used to relieve anxiety, excitement, restlessness or even mental disorder. * [[Ephedrine]] and [[Phenylephrine]], as amine hydrochlorides, are used as decongestants. * [[Amphetamine]], [[Methamphetamine]], and [[Methcathinone]] are amines that are listed as controlled substances by the [[Drug Enforcement Agency|DEA]]. * [[Amitriptyline]], [[Imipramine]], [[Lofepramine]] and [[Clomipramine]] are [[tricyclic antidepressant]]s and tertiary amines * [[Nortriptyline]], [[Desipramine]], and [[Amoxapine]] are tricyclic antidepressants and secondary amines * (The tricylics are grouped by the nature of the final amine group on the side chain.) ===Gas Treatment=== * Aqueous [[monoethanolamine]] (MEA), diglycolamine (DGA), [[diethanolamine]] (DEA), diisopropanolamine (DIPA) and [[MDEA|methyldiethanolamine]] (MDEA) are widely used industrially for removing [[carbon dioxide]] (CO<sub>2</sub>) and [[hydrogen sulfide]] (H<sub>2</sub>S) from natural gas streams and refinery process streams. They may also be used to remove CO<sub>2</sub> from combustion gases / flue gases and may have potential for abatement of greenhouse gases. == See also == * [[IUPAC_nomenclature_of_organic_chemistry#Amines_and_Amides|IUPAC nomenclature]] for the official naming rules for amines. * [[Biogenic amine]] * [[Acid-base extraction]] * [[Amine gas treating]] ==References== {{Reflist}} {{Functional Groups}} [[Category:Amines|*]] [[ar:أمين]] [[bn:অ্যামিন]] [[ca:Amina]] [[cs:Aminy]] [[de:Amine]] [[et:Amiinid]] [[es:Amina]] [[eo:Amino]] [[fr:Amine (chimie)]] [[hr:Amin]] [[it:Ammine]] [[he:אמין]] [[ka:ამინები]] [[lv:Amīni]] [[hu:Aminok]] [[mk:Амин (хемија)]] [[nl:Amine]] [[ja:アミン]] [[no:Amin]] [[nn:Amin]] [[oc:Amina]] [[pl:Aminy]] [[pt:Amina]] [[ro:Amină]] [[ru:Амины]] [[sk:Amín]] [[fi:Amiini]] [[sv:Amin]] [[ta:அமைன்]] [[vi:Amin]] [[tr:Amin]] [[uk:Аміни]] [[zh:胺]]