Txhua chav kawm ntawm cov tshuaj sib xyaw muaj peev xwm nthuav tawm cov khoom vim lawv cov qauv hluav taws xob. Alkanes yog tus cwj pwm los ntawm kev hloov pauv, tshem tawm lossis oxidation tshwm sim ntawm cov molecules. Tag nrho cov txheej txheem tshuaj muaj lawv tus kheej cov yam ntxwv ntawm cov ntws, uas yuav tau tham ntxiv.
Dab tsi yog alkanes
Cov no yog cov saturated hydrocarbon compounds hu ua paraffins. Lawv cov molecules tsuas muaj carbon thiab hydrogen atoms, muaj ib tug linear los yog branched acyclic saw, nyob rau hauv uas muaj tsuas yog ib lub tebchaw. Muab cov yam ntxwv ntawm cov chav kawm, nws tuaj yeem suav cov kev cuam tshuam dab tsi ntawm alkanes. Lawv ua raws li cov qauv qhia thoob plaws hauv chav kawm: H2n+2C.
Cov qauv tshuaj
Paraffin molecule muaj xws li carbon atoms qhia sp3-hybridization. Lawv muaj tag nrho plaub lub valence orbitals muaj tib lub cev, lub zog thiab kev taw qhia hauv qhov chaw. Qhov loj ntawm lub kaum sab xis ntawm lub zog yog 109 ° thiab 28'.
Qhov muaj ib daim ntawv cog lus hauv cov molecules txiav txim siab seb qhov twg tshwm simCov yam ntxwv ntawm alkanes. Lawv muaj σ-compounds. Kev sib raug zoo ntawm cov pa roj carbon monoxide yog nonpolar thiab tsis muaj zog polarizable, thiab yog me ntsis ntev dua hauv C-H. Kuj tseem muaj kev hloov pauv hauv cov hluav taws xob ntom ntom rau cov pa roj carbon atom, uas yog cov electronegative tshaj plaws. Raws li qhov tshwm sim, C-H compound yog tus cwj pwm los ntawm polarity tsawg.
Kev hloov pauv hloov pauv
Cov khoom ntawm cov chav kawm paraffin muaj cov tshuaj tsis muaj zog. Qhov no tuaj yeem piav qhia los ntawm lub zog ntawm daim ntawv cog lus ntawm C-C thiab C-H, uas nyuaj rau kev tawg vim tsis muaj polarity. Lawv qhov kev puas tsuaj yog nyob ntawm homolytic mechanism, uas cov dawb-hom radicals koom. Tias yog vim li cas alkanes yog tus cwj pwm los ntawm kev hloov pauv. Cov khoom zoo li no tsis tuaj yeem cuam tshuam nrog cov dej molecules lossis cov ions them nqi.
Lawv suav nrog kev hloov pauv dawb radical, uas hydrogen atoms hloov los ntawm cov ntsiab lus halogen lossis lwm pab pawg. Cov tshuaj tiv thaiv no suav nrog cov txheej txheem cuam tshuam nrog halogenation, sulfochlorination thiab nitration. Lawv qhov tshwm sim yog kev npaj ntawm alkane derivatives.
Lub tshuab ntawm kev hloov pauv dawb radical yog ua raws li peb theem tseem ceeb:
- Cov txheej txheem pib nrog kev pib lossis nucleation ntawm cov saw hlau, vim tias cov dawb radicals tsim. Cov catalysts yog ultraviolet lub teeb qhov chaw thiab tshav kub.
- Tom qab ntawd cov saw hlau tsim, uas ua tiav kev sib cuam tshuam ntawm cov khoom nquag nrog cov tsis muaj zog molecules tshwm sim. Lawv hloov mus rau hauv molecules thiab radicals, feem.
- kauj ruam kawg yog ua kom cov saw hlau tawg. Recombination lossis ploj ntawm cov khoom nquag raug pom. Qhov no tso tseg txoj kev loj hlob ntawm cov tshuaj tiv thaiv kab mob.
txheej txheem Halogenation
Nws yog ua raws li cov txheej txheem ntawm hom radical. Cov tshuaj tiv thaiv halogenation ntawm alkanes tshwm sim los ntawm ultraviolet irradiation thiab cua sov ntawm ib tug sib tov ntawm halogens thiab hydrocarbons.
Txhua theem ntawm cov txheej txheem yog ua raws li txoj cai hais los ntawm Markovnikov. Nws hais tias, ua ntej ntawm tag nrho cov, lub hydrogen atom, uas belongs rau feem ntau hydrogenated carbon, yog raug hloov los ntawm ib tug halogen. Halogenation pib ua raws li hauv qab no: los ntawm tertiary atom mus rau thawj carbon.
Cov txheej txheem zoo dua rau alkane molecules nrog cov saw hlau ntev ntev. Qhov no yog vim qhov txo qis hauv ionizing zog hauv qhov kev taw qhia, ib qho hluav taws xob yooj yim dua los ntawm cov khoom.
Ib qho piv txwv yog chlorination ntawm methane molecule. Qhov kev txiav txim ntawm ultraviolet ua rau kev sib cais ntawm cov tshuaj chlorine rau hauv radical hais tawm tsam cov alkane. Muaj ib qho detachment ntawm atomic hydrogen thiab tsim ntawm H3C· los yog methyl radical. Xws li ib tug hais, nyob rau hauv lem, tawm tsam molecular chlorine, ua rau kev puas tsuaj ntawm nws cov qauv thiab tsim ib tug tshiab tshuaj reagent.
Tsuas yog ib qho hydrogen atom hloov ntawm txhua theem ntawm cov txheej txheem. Cov tshuaj tiv thaiv halogenation ntawm alkanes ua rau maj mam tsim ntawm chloromethane, dichloromethane, trichloromethane thiab carbon tetrachloride molecules.
Schematically, cov txheej txheem zoo li no:
H4C + Cl:Cl → H3CCl + HCl, H3CCl + Cl:Cl → H2CCl2 + HCl, H2CCl2 + Cl:Cl → HCl3 + HCl, HCCl3 + Cl:Cl → CCl4 + HCl.
Tsis zoo li cov tshuaj chlorination ntawm methane molecule, ua cov txheej txheem zoo li no nrog lwm cov alkanes yog tus cwj pwm los ntawm kev tau txais cov tshuaj uas hloov cov hydrogen tshwm sim tsis yog ntawm ib qho atom carbon, tab sis ntawm ob peb. Lawv qhov sib piv ntau yog txuam nrog qhov ntsuas kub. Nyob rau hauv cov xwm txheej txias, muaj qhov txo qis ntawm kev tsim cov derivatives nrog cov qauv tertiary, theem nrab thiab thawj.
Nrog rau qhov kub thiab txias, tus nqi ntawm kev tsim ntawm cov tebchaw zoo li no tawm. Cov txheej txheem halogenation yog cuam tshuam los ntawm qhov zoo li qub, uas qhia txog qhov sib txawv ntawm qhov sib txawv ntawm qhov sib tsoo nrog cov pa roj carbon atom.
Cov txheej txheem ntawm halogenation nrog iodine tsis ua raws li ib txwm muaj. Nws yog ib qho tsim nyog los tsim cov xwm txheej tshwj xeeb. Thaum methane raug rau cov halogen no, hydrogen iodide yog tsim. Nws raug cuam tshuam los ntawm methyl iodide, vim li ntawd, thawj zaug reagents raug tso tawm: methane thiab iodine. Cov tshuaj tiv thaiv zoo li no suav tias yog thim rov qab.
Wurtz tshuaj tiv thaiv rau alkanes
Yog ib txoj hauv kev kom tau txais cov hydrocarbons saturated nrog cov qauv symmetrical. Sodium hlau, alkyl bromides los yog alkyl chlorides yog siv los ua reactants. NtawmLawv kev sib cuam tshuam ua rau sodium halide thiab txuas ntxiv hydrocarbon saw, uas yog qhov sib npaug ntawm ob lub hydrocarbon radicals. Schematically, cov synthesis yog raws li nram no: R−Cl + Cl−R + 2Na → R−R + 2NaCl.
Cov tshuaj tiv thaiv Wurtz rau alkanes tsuas yog ua tau yog tias cov halogens hauv lawv cov molecules nyob ntawm thawj carbon atom. Piv txwv li, CH3−CH2−CH2Br.
Yog tias cov khoom sib xyaw halocarbon ntawm ob lub tebchaw koom nrog hauv cov txheej txheem, ces peb cov khoom sib txawv yog tsim thaum lub sij hawm condensation ntawm lawv cov chains. Ib qho piv txwv ntawm xws li cov tshuaj tiv thaiv ntawm alkanes yog kev sib cuam tshuam ntawm sodium nrog chloromethane thiab chloroethane. Cov zis yog sib xyaw uas muaj butane, propane thiab ethane.
Ntxiv rau sodium, lwm cov hlau alkali tuaj yeem siv tau, uas suav nrog lithium lossis potassium.
txheej txheem sulfochlorination
Nws tseem hu ua Reed cov tshuaj tiv thaiv. Nws ua raws li lub hauv paus ntsiab lus ntawm kev hloov pauv dawb radical. Qhov no yog yam ntxwv ntawm cov tshuaj tiv thaiv ntawm alkanes rau qhov kev txiav txim ntawm kev sib xyaw ntawm sulfur dioxide thiab molecular chlorine nyob rau hauv lub xub ntiag ntawm ultraviolet hluav taws xob.
Cov txheej txheem pib nrog kev pib ntawm cov saw hlau, uas ob lub radicals tau los ntawm cov tshuaj chlorine. Ib tug ntawm lawv tawm tsam cov alkane, ua rau ib hom alkyl thiab hydrogen chloride molecule. Sulfur dioxide txuas mus rau hydrocarbon radical los tsim ib tug complex particle. Rau stabilization, ib qho chlorine atom raug ntes los ntawm lwm cov molecule. Cov khoom kawg yog alkane sulfonyl chloride, nws yog siv rau hauv cov synthesis ntawm deg-active compounds.
Schematically, cov txheej txheem zoo li no:
ClCl → hv ∙Cl + ∙Cl, HR + ∙Cl → R∙ + HCl, R∙ + OSO → ∙RSO2, ∙RSO2 + ClCl → RSO2Cl + ∙Cl.
txheej txheem ntsig txog nitration
Alkanes hnov mob nrog nitric acid nyob rau hauv daim ntawv ntawm 10% tov, nrog rau tetravalent nitrogen oxide nyob rau hauv lub gaseous lub xeev. Cov xwm txheej rau nws cov dej ntws yog qhov ntsuas kub ntawm qhov ntsuas kub (txog 140 ° C) thiab ntsuas qhov ntsuas qis. Nitroalkanes yog tsim los ntawm cov zis.
Cov txheej txheem dawb radical no tau muab npe tom qab tus kws tshawb fawb Konovalov, uas tau tshawb pom cov synthesis ntawm nitration: CH4 + HNO3 → CH 3NO2 + H2O.
Cleavage mechanism
Alkanes yog tus cwj pwm los ntawm dehydrogenation thiab tawg cov tshuaj tiv thaiv. Lub methane molecule tau ua tiav thermal decomposition.
Lub ntsiab mechanism ntawm cov kev tshwm sim saum toj no yog kev tshem tawm ntawm atoms ntawm alkanes.
Dehydrogenation txheej txheem
Thaum hydrogen atoms raug cais tawm ntawm cov pob txha ntawm cov pa roj carbon monoxide, tshwj tsis yog cov methane, cov tshuaj tsis txaus ntseeg tau txais. Cov tshuaj tiv thaiv zoo li no ntawm alkanes tshwm sim ntawm qhov kub thiab txias (ntawm 400 txog 600 ° C) thiab nyob rau hauv kev cuam tshuam ntawm accelerators nyob rau hauv daim ntawv ntawm platinum, npib tsib xee, chromium thiab txhuas oxides.
Yog tias propane lossis ethane molecules koom nrog cov tshuaj tiv thaiv, ces nws cov khoom yuav yog propene lossis ethene nrog ib daim ntawv cog lus ob npaug.
Thaum dehydrogenating plaub lossis tsib lub cev pob txha, tuagkev sib txuas. Butane yog tsim los ntawm butadiene-1, 3 thiab butadiene-1, 2.
Yog cov tshuaj uas muaj 6 lossis ntau dua carbon atoms nyob rau hauv cov tshuaj tiv thaiv, ces benzene yog tsim. Nws muaj cov tub ntxhais uas muaj ntxhiab nrog peb ob daim ntawv cog lus.
txheej txheem decomposition
Nyob rau hauv cov xwm txheej ntawm qhov kub thiab txias, cov tshuaj tiv thaiv ntawm alkanes tuaj yeem tshwm sim nrog kev rhuav tshem cov pa roj carbon monoxide thiab tsim cov khoom nquag ntawm hom radical. Cov txheej txheem zoo li no hu ua cracking lossis pyrolysis.
Cua sov cov reactants rau kub tshaj 500 ° C ua rau decomposition ntawm lawv cov molecules, thaum lub sij hawm uas complex sib tov ntawm alkyl-hom radicals yog tsim.
Kev nqa tawm cov pyrolysis ntawm alkanes nrog ntev carbon chains nyob rau hauv cov cua sov muaj zog yog txuam nrog tau txais saturated thiab unsaturated compounds. Nws yog hu ua thermal cracking. Cov txheej txheem no tau siv mus txog rau nruab nrab ntawm lub xyoo pua 20th.
Qhov tsis zoo yog kev tsim cov hydrocarbons nrog tus lej octane qis (tsis pub ntau tshaj 65), yog li nws tau hloov los ntawm catalytic cracking. Cov txheej txheem yuav siv sij hawm qhov chaw nyob rau hauv lub kub tej yam kev mob uas yog qis dua 440 ° C thiab pressures hauv qab 15 atmospheres, nyob rau hauv lub xub ntiag ntawm ib tug aluminosilicate accelerator nrog tso tawm ntawm alkanes muaj ib tug branched qauv. Ib qho piv txwv yog methane pyrolysis: 2CH4 →t°C2 H2+ 3H2. Thaum cov tshuaj tiv thaiv no, acetylene thiab molecular hydrogen raug tsim.
Methane molecule tuaj yeem hloov pauv. Cov tshuaj tiv thaiv no xav tau dej thiab nickel catalyst. Nyob ntawmCov zis yog sib xyaw ntawm carbon monoxide thiab hydrogen.
txheej txheem oxidation
Cov tshuaj lom neeg cov yam ntxwv ntawm alkanes koom nrog kev pub dawb ntawm electrons.
Nws pib-oxidation ntawm paraffins. Nws koom nrog cov txheej txheem dawb-radical rau oxidation ntawm saturated hydrocarbons. Thaum cov tshuaj tiv thaiv, hydroperoxides tau los ntawm cov kua theem ntawm alkanes. Nyob rau theem pib, paraffin molecule cuam tshuam nrog oxygen, vim li ntawd, cov radicals nquag tawm. Tsis tas li ntawd, lwm molecule O2 cuam tshuam nrog alkyl particle, ua rau ∙ROO. Ib qho alkane molecule hu rau fatty acid peroxide radical, tom qab uas hydroperoxide tso tawm. Ib qho piv txwv yog autoxidation ntawm ethane:
C2H6 + O2 ∙C2 H5 + HOO∙, ∙C2H5 + O2 ∙OOC 2H5, ∙OOC2H5 + C2H6 → HOOC2H5 + ∙C2H5.
Alkanes yog tus cwj pwm los ntawm cov tshuaj tiv thaiv combustion, uas yog ib qho ntawm cov tshuaj lom neeg tseem ceeb thaum lawv txiav txim siab hauv cov roj muaj pes tsawg leeg. Lawv muaj cov cim oxidative nrog kev tso cua sov: 2C2H6 + 7O2 → 4CO 2 + 6H2O.
Yog tias muaj cov pa me me hauv cov txheej txheem, ces cov khoom kawg yuav yog cov thee lossis carbon divalent oxide, uas yog txiav txim siab los ntawm qhov concentration ntawm O2.
Thaum alkanes raug oxidized nyob rau hauv lub zog ntawm catalytic tshuaj thiab rhuab mus rau 200 ° C, molecules ntawm cawv, aldehyde los yogcarboxylic acid.
Ethane piv txwv:
C2H6 + O2 → C2 H5OH (ethanol),
C2H6 + O2 → CH3 CHO + H2O (ethanal thiab dej), 2C2H6 + 3O2 → 2CH3 COOH + 2H2O (ethanoic acid thiab dej).
Alkanes tuaj yeem oxidized thaum raug rau peb tus tswvcuab cyclic peroxides. Cov no suav nrog dimethyldioxirane. Qhov tshwm sim ntawm oxidation ntawm paraffins yog cawv molecule.
Cov neeg sawv cev ntawm paraffins tsis hnov qab KMnO 4 lossis potassium permanganate, nrog rau cov dej bromine.
Isomerization
Ntawm alkanes, hom tshuaj tiv thaiv yog tus cwj pwm los ntawm kev hloov pauv nrog lub tshuab electrophilic. Qhov no suav nrog isomerization ntawm cov saw hlau carbon. Cov txheej txheem no yog catalyzed los ntawm txhuas chloride, uas cuam tshuam nrog saturated paraffin. Ib qho piv txwv yog isomerization ntawm butane molecule, uas dhau los ua 2-methylpropane: C4H10 → C3. H7CH3.
Fragrance process
Saturates nrog rau los yog ntau dua carbon atoms nyob rau hauv lub ntsiab carbon saw muaj peev xwm dehydrocyclization. Xws li cov tshuaj tiv thaiv tsis raug rau cov molecules luv. Qhov tshwm sim yog ib txwm muaj rau lub nplhaib nyob rau hauv daim ntawv ntawm cyclohexane thiab nws cov derivatives.
Nyob rau hauv lub xub ntiag ntawm cov tshuaj tiv thaiv accelerators, ntxiv dehydrogenation tshwm sim thiabtransformation mus rau hauv ib tug ruaj khov benzene nplhaib. Acyclic hydrocarbons hloov mus rau cov tshuaj tsw qab los yog arenes. Ib qho piv txwv yog dehydrocyclization ntawm hexane:
H3C−CH2− CH2− CH 2-CH2-CH3 → C6H 12 (cyclohexane), C6H126H6+ 3H2 (benzene).
