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7/31/2019 K THUT XC TC-XTDongthe

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K THUT XC TC

XC TC NG TH ThS. DipKhanh

TRNG I HC B RA VNG TU KHOA HA HC V CNTP


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Xc tc ng th?

u im caxc tc ng th C chn lcv hottnh cao hnso vixc tc d th.iu kin tinhnh phn ng mm hn.Do khng c qu trnh khuchtn mao qun(v chtxc tc ha trongcht phn ng). V vy, y ch c vn l s chuyn khi giaphakh v pha lng(s b trittiu theo s khuy trnl tng).Qua trnh truyn nhit ddng, khng xyra trng hpnng cc b.C ch ca phn ngha hc d biu din hn, n gin hn.Qu trnh tinhnh phn ng dthao tc hn.

Xc tc ng th c th l xc tc axt baz , xc tc enzym, xc tc phc .

Nhc im Qu trnh phn ng thnggin onnn khng t ngha c.Nng sut thit bkhng cao v dgy n mn thit b.Qu trnh tch xc tc ra khi phn ng rt kh khn.Phmvi p dng hp.


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Phn chia cc loi phn ng ng th

Phn ng ng thpha kh.Phn ng ng thpha lng.Phn ng ng thpha lng.


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2005 Noble Prize in Chemistry
http://localhost/var/www/apps/conversion/GeneralKnowledge/NobelprizeChemistry2000-2007/NobelPrize2005.pdfhttp://localhost/var/www/apps/conversion/GeneralKnowledge/NobelprizeChemistry2000-2007/NobelPrize2005.pdf


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Phn ng2: sunfon ha benzen trong dung dch xyra theoc chsau

Phn ng3: chuyn v Pinacolic


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Phng trnh ng hc ca phn ng xc tcng th

Nuqu trnh tora HCTG l giai an chmth vn tc ca phn ng c vittheo V 1.Nuqu trnh phn hyHCTG l giai an chmth vn tc ca phn ng c vittheo V 2.

31

2

1 1

2 3

,

(2)

.

Ta co phan ng: xuc tac K (1)

C che nh sau: nA + K

Van toc tao thanh HCTG:Van toc phan huy HCTG:

k k

k

n A K

Z

nA mB

Z mB K

V k C C

V k C


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Phn ng xc tc ng th, xc tc Axt- Baz

Phn lncc phn ngxc tc ng th cxc tc bicc axit v baz . Trong , nhiu phn ng c xc tc bi axit protonic ( nh HF, H 2SO 4,H3PO 4,) v mt s cxc tc bngcc axitLewis( nhBF 3, AlCl 3, SnCl 2,)

V d: Phan ng Protonic: AH + B A + BHPhan ng axit-baz Lewis:


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S ph thuc hng s tc k vo pH camitrng.

Tc ca phn ngxc tc axt- baz ph thuc rt ln vo pH cami trng. V vym mt phn ngxc tcaxit-bazo thngc ba phn ng xyra song song:

Phn ngdo xc tc axit.Phn ngdo xc tc baz .Phn ngdo va chm giacc phn t phn ng

Do vy vn tcchung ca phn ng s bng tng vn tc ca ba phn ngtrn.V d: phn ng nphn t: S1 S2

1 3

1

[ ].[ ]

[ ].[ ]

Vi xuc tac axit, ta co: V =k

Vi xuc tac bazo, ta co: V =ka H

b OH

S H O

S OH


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Trong phn ng ng thxc tc axit- baz thngc cc trng hp sau

0 1 3 1 0 1

1

3 0

[ ].[ ] [ ].[ ] [ ]

[ ], [ ] [ ]

Vay, van toc chung cua ca phan ng:V V V V k k k

vi k k k k

c a b H OH

c

c H OH

S H O S OH S

k S H O OH


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ng hc ca phn ngxc tc axt- baz Trng hp xc tcl axt, xt phn ng:

1

'1

2

'

2

3

1 2 1 2

1 1

1 2 1 2

2 2

(1)

(2)

(3)

Gia s phan ng xay ra theo c che sau

S

AH

k

k

k

k

k

S S P P

AH S H A

S H S P P H

P H A P AH


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4

5

2 3

3 2

(4)

(5)

+2

2

+2 2

Neu HCTG (P H ) co tac dung manh vi moi trphan ng (H O) th c che se i theo mot hng

P H Pk

k

H O H O

H O A H O AH

C che cua phan ng tren co the xay ra theo 2hp: c che 1 gom cac phan ng 1,2,3; c che 2

cac phan ng 1,2,4,5. e xac nh van toc cung ta phai gia s cac giai oan (phan ng) lala cac giai oan cham. Cu the


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C ch1: gmcc giai on1,2, 3.Gi thitgiai on1 chm, giai on2, 3 nhanhGi thitgiai on2 chm, giai on1, 3 nhanh

Gi thitgiai on3 chm, giai on1, 2 nhanh

C ch2: giai on1, 2, 4, 5.Gi thitgiai on4 chm, giai on1, 2, 5 nhanh

1 1 1[ ][ ]cV V k S AH

2 2 1 2 3[ ][ ][ ] I

ca

K V V k S S H O

K

1 23 3

1

[ ][ ][ ]c I II

S S AH V V k K K

P

1 2 3

4 4 1

[ ][ ][ ]1c I II

a

S S H OV V k K K

K P


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Trng hpxc tc l baz , xt phn ng

1

1

2

2

3

4

5

1 2 1 2

1 1

1 2 2 1

2 2

2 2 2

2

(1)

(2)

(3)

(4)(5)

C che e ngh nh sau

Neu dung moi b proton hoa

Ta cung tien hanh gia thiet nh

k

k

k

k

k

k

k

S H S P P H

S H B S BH

S S P P

P BH P H B

P H O P H OH

OH BH H O B

oi xuc tac laaxt e xac nh bieu thc van toc phan ng


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Giai on1 chm

Giai on2 chm

Giai on3 chm

Giai on4 chm

1 1 1[ ][ ]cV V k S H B

2 2 1 2[ ][ ]cV V k S S

1 23 3

1

] ][ ][ [[ ]c I II

S H S BV V k K K

P

4 4 1 21

1 [ ]] ][ [ [ ]c I II aOH

V V k K K S H S K P


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Tnh lcaxt- baz Ni chung lcaxt- baz cng cao th hottnh xc tc cngmnh.

Lcaxt: tnh lcaxt ta cho axt tc dng vi nc

Theo Bronsted, lcaxt l hng s tc ca phngtrnh(6), k hiul k a.

2 3 (6) AH H O A H O

.

vi a va (0<


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Lc baz : cho baz tc dng vi nc

Theo Bronsted, lc baz l hng s tc ca phngtrnh(7), k hiul k b.

(7)+ -

2B + H O BH + OH

'

'

. .

.

.

vi a va (0<


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Tnh gi tr ca v 2 3

'3 3

' 3

.[ ] . .[ ]

.[ ][ ] . .[ ][ ]

[ ][ ]. . .

[ ]

thuan

nghch

thuan nghch

Khi can bang cha thiet lap, ta coV

V

Khi can bang thiet lap, ta co: V V

a a

b a

a a

AH H O A H O

k AH a K AH

k A H O b K A H O

A H Oa K b K

AH

'

' 1

1[1 ( )]

'

'

. .

. .

1Neu a b ta co:

a a

a a

aa

a

b K K

a K b K

K aK

b K


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Trng hpaxt- baz nhiu chc(m, n chc) th hng s axt v hng s baz sl:

,

,

..

a m a

b n b

k m k k n k

Hot v h s hot Hng saxt cxc nh davo nng , nhng ch milnhtnh. nh lng cn phidng hot .V tr s, hot (a) bng nng nhn vi h sf, gil h s hot .Cng thcton hc nhsau: a = C.f

i vidung dchv cng long th nng bng hot (a = C).i vidung dch thc, do lc tngtc giacc ion th hin mnhnn hot s nh hn nng .


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V d: xt phn ng

Lc ny hng saxt K a ca phn ng tr thnh2 3 AH H O A H O

3 3

3

3

3

. . .

.

...

[ ] [ ][ ]

[ ][ ]

[ ]

H O A H O Aa

AH AH

H O Aa

AH

a a H O f A f K a AH f

f f H O AK

AH f


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Phn ngxc tc axt- baz cho nhn in t .Quan im caLewis

Axt Lewis cng b trung ha ging nhaxt Bronsted.

Qu trnh trung ha nhanh v khng i hi nng lng.C thtch axt Lewis ra thnh cc axt v baz yu.


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Axt Lewis c th lm xc tc cho nhng phn ng m

trc ydng xc tc Bronsted, hottnh cao, c bit chn lccao.

Cc loiAxt Lewis l: HF, AlCl 3, AlBr 3, BF 3, SnCl 4,ZnCl

2, Al

2O

3.

Lcaxt Lewis c th nhn bit bngcc ch thmu.

i viaxt Bronsted, nng lngtch proton khng i,khng ph thucvo mi trng. Cn i viaxt Lewis,nng lngtch cp in t ph thucvo i tng nhn in t.


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C ch phn ngkhi dng xc tc axt LewisPhn ngFridel-Kraft: alkyl ha vng thm bng hp cht HX c mtxc tc AlCl 3.

C ch nhsau:

Ion cacbocation (R +) kt hp vivng benzen


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Phn ngalkyl vng thm bngolefin: xc tc AlCl 3.

Trong mi trng nc, axt Lewis kt hp vi ncchoProton. Kt qu tora axt proton c tnh axt mnh hnsovicc hp chtaxt khc.

3 2 3[ ] AlCl H O AlCl OH H


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Hiu ng mui Thc nghim ch rngkhi thm mui caaxt (axt l xc tc)

vo phn ngxc tc ng thth lm cho vn tc phn ng tng ln r rt. Hiu ng ny gi l hiu ng mui bc2(Hiu ng mui th cp).

V d: s ph thuc vn tc ca phn ngvo lng muiNatri Acetatthm vo trong phn ng cxc tc bngaxt acetic theo Dawson vCarter khi khost phn ngiod ha aceton.


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Arrhenius cn nhn thy rng, khi thm muitrung tnh cion khc vi ion caaxt lm xc tc th vn tc phn ng cng tng ln. Hiu ng ny gi l hiu ng mui bc1(Hiu ng mui s cp).

V d:


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Giithch hiu ng mui th cp Theo thuyt inly c in, nuxc tc l axt yuth s phn ly theo phngtrnh

Theo l thuyt, sthm ion A - slm gim sphn ly ca axt AH nn slm gimtc dng caxc tc. Vy tisaotrong trng hpny lilm tng vn tc ca phn ng???

2 3

+ -+ - -

3 b a n 2H OH

Ta co phng trnh van toc tong quat

V=k [H O ] + k [A ] + k [AH] + k [OH ] + k [H O]

AH H O A H O


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Giithch hiu ng mui s cp Victhm cc ion khc viion caaxt khng nh hnggn sphn ly caaxt. Vy tisao lic tc dnglm thayi vn tc ca phn ng???Theo Arrhenius th khi thm muic ion khc th s lmthay i lcion cadung dch. Trong trng hpny, nng ion tham gia phn ngkhng quyt nh s thay i tc

phn ngm chnh do sthay i h s hot caccion quyt nh.Xt v d: ][ A B AB P

.. .

.] . ] . . ] . (**)

[ ][ ].[ ]

[ [ [ ] [ [ ]

AB ABa

A B A B

A Ba a

AB

a f ABK a a A B f f

f f AB K A B K A B F

f


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Giai on tc nhl giai onphn hyHCTG nn:

T y ta xc nh c hng s tc thc nghim ca phn ngtrn l:

Theo Debye-Huckel, h s hot caion trong dung dch c lin quan nha tr v lcion ( ) cadung dch nh sau:

2 ][cV k AB

2 2

2 0

] . . ] .

. . .

[ [ [ ]c atn a

V k AB k K A B F

k k K F k F

2

lg1

ii

Z A f C

Ba

lg .1

n m

m n

A B

A B

hay

A z z f C

Ba


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i vi nhngion ring bit, h s hot khng thay i.Thc nghimcho thy s ph thuc ca h s hot volcion. Trong phmvi lcion ln(t0,1-0,5) th gi tr C. rt nh. Lc ny ta c:

Trong o: he so hoat oZ hoa tr cua ion

a ng knh gan ung cua ionA, B, C hang so phu thuoc bi ai lng ham

so lng cc cua dung dch va nhiet oC hang so thc n

i

i

f

20,5 . )

ghiem

lc ion ( i iC Z

2

lg1

ii

Z A f

Ba

lg

1

n m

m n

A B A B

hay

A z z f

Ba


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Khi lcion nh(


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Suy ra hng s thc nghim ca phn ng

Khi dung mi l ncv 25oC th A=0,509, nn ta c:

lg lg g g A B ABF f f f

0

0

lg lg lg

lg lg 2 .

( : Bronsted Berrom)

tn

tn A B

k k F

k k A Z Z

Pt

0

0

lg lg lg

lg lg 1,18 .

tn

tn A B

k k F

k k Z Z

2 2 2

2 2 2 2lg ( )

lg ( 2 . )

lg 2 .

[ ] A B A B

A B A B A B

A B

F A Z Z Z Z

F A Z Z Z Z Z Z

F A Z Z


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T phngtrnh Bronsted Berrom v pt (**) ta suy ra:

NuZA hocZB bng0, th [AB] khng i. NuZA .ZB > 0 th [AB] tngkhi tng. NuZA .ZB < 0 th [AB] gimkhi tng.

Hiu ng mui s cp c tora do s bin i nng ca phc chttrung gian ( thng qua lcion).

Lu : Phng trnh Bronsted Berrom ch ng trong khu vcmnng cht inly thamn phng trnh Debye Huckel, tclkhong nng 5.10 -3 M.

2

] . ] .10[ [ [ ]A B AZ Z

a AB K A B


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Tng hp L-dopa


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