phan ung axit bazo 2012 day cao hoc ban dung.pptx

8/10/2019 phan ung axit bazo 2012 day cao hoc ban dung.pptx

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CH NG I:CC THUYT AXIT BAZ TS. Tr ng Th Cm Mai

Khoa Ha hc HQuy Nhn

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THUYTAXIT BAZ CAARENIUYT

- Axit l cht tan trong n c phn ly cho ion H +.- Ba z l cht tan trong n c phn ly cho ion OH - - Phn ng trung ha l phn ng gia axit v baz ,to ra mui v n c .- Phn ng thy phn ca mui l phn ng gia ionca mui vi n c , kt qu lm cn bng phn li ca

n c thay i, dn n mi tr ng ca dung dch thayi.

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u im:Thuyt ca Areniuyt l thuyt axitbaz sm nht.

N gii thch c nhiu tnh cht v phn ng ca ccaxit, baz trong dung dch n c .

Nhc im:- Thuyt axit baz Areniuyt ch p dng ng cho

dung mi l n c , khng p dng c cho tt c ccdung mi, ng thi n ch a thy c vai tr quyt nh ca dung mi trong s phn li axit, baz .

- Thuyt Areniuyt khng gii thch c cc phn

ng to ra mui ging nh phn ng trung ha m trong li khng c H + hoc OH - tham gia.

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Axit l cht (hoc ion) c kh nng cho proton, baz lcht (hoc ion) c kh nng nhn proton.V d:

CH3COOH + H

2O CH

3COO - + H

3O + (a)

Axit Baz Baz Axit

Cp CH3COOH CH3COO- v cp H3O+ - H2O l nhng cp axit-baz lin hp.

A1 + B 2 B1 + A 2 Axit 1 baz 2 baz 1 axit 2

THUYT AXIT- BAZ CA BRONSTET VLAURI ( thuyt proton)

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Cc axit Bronstet-Lauri u cha proton chngcn c gi l axit protonic.

Cc axit protonic c th l:- Phn t trung ha nh HCl, H 2SO4 , H 3PO 4 - Anion nh HSO 4- , H 2PO 4- , HS - - Cation nh H3O+ , NH 4+ , [Pt(NH 3) 6] 4+ ,

[Fe(H 2O) 6] 3+ Cc baz Bronstet-Lauri c th l:

- Phn t trung ha nh NH3 , R-NH 2 , R 2CO (Rl gc hu c hoc halogen), piridin, H 2O - Anion nh H2PO 4- , OH - , Cl - , NH 2-

- Cation nh H2N-NH 3+ , [Pt(NH 3) 5(OH)] 3+ ,[Fe(H 2O) 5(OH)] 2+

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u im :1. Thuyt proton gii thch c tnh cht baz ca cc hp cht hu c nh amin, ete, xeton vthioete Nh c cc cp electront do, khi kt hp proton, cc hp cht ny to thnh cc cationoni.

Nhng ion ny l axit lin hp ca cc hp cht .

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Nh c im:Thuyt proton ch gii hn cho nhng phn ng axit-baz trong c s trao i proton . C nhiu qu trnht ng tc, trong cc cht th hin tnh cht axit vtnh cht baz , nh ng theo thuyt proton khng cho lphn ng axitbaz , bi v khng c s trao i

proton. Chng hn, phn ng ca oxit kim loi v oxitphi kim to ra mui.Th d:CaO + SO 3 CaSO 4

Hoc phn ng gia SOCl 2 v K 2SO 3 trong SO 2 lng:SOCl 2 + K 2SO 3 2KCl + 2SO 2

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Lc axit c tr ng cho kh nng phn lyproton ca axit, lc baz c tr ng cho kh nng nhn proton ca cc baz.

Trong iu kin dung mi l n c lc axitbaz theo Bronstet Laury ph thuc vo ccyu t: phn cc ca lin kt ( da vo hiu ng

m in ). bn ca lin kt ( da vo bn k nh nguynt , di lin kt nng lng lin kt , mt in tch dng hoc m )

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Cc yu t nh h ng n lc axit baz Bronstet Laury


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Trong phn nhm chnh :+ Khi i t trn xung d i yu t quyt

nh n lc axit ca cc hirua phi kim l dilin kt. V i t trn xung bn knh ca E tng,lm cho di lin kt E H tng, bn ca linkt gim nn kh nng tch H+ tng.

+ V d dy HF HI, r X tng t F I nnnng lng lin kt gim t HF HI (HF l 569kJ/mol trong khi nng lng lin kt HI ch l 297kJ/mol ) bn ca lin kt HXgim v vy lc

axit tng t HF HI.( y ta khng th cn c vo phn cc ca lin kt so snh lc axit mc d lin kt HF phn cc hn lin kt HI).

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- i vi dy hiroxit : c 2 kiu phn ct lin kt Kiu 1: R O H ROH th hin tnh axit.Kiu 2: R O H ROH th hin tnh baz.

Trong mt chu k : + Khi i t tri sang phi, m in ca R

tng, hiu m in R O gim, lin kt R OH tr thnh lin kt cng ha tr. iu ny dn n lin kt O H phn cc n mc H+ tch ra d, lc axit tng.

+ Khi i t tri sang phi bn knh R cnggim, mt in tch d ng trn R cng ln, R+ vH+ y nhau cng mnh lm cho kh nng tch H+ tng lc axit tng.

b. Axit baz cha oxi

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Trong mt phn nhm chnh: + Khi i t trn xung m in ca R

gim, hiu m in R O tng, lin kt R Oc th xem l lin kt ion nn chng d phn lithnh OH -, lc axit gim.

+ Bn knh ca R tng, in tch ca Rkhng i dn n + gim, kh nng y H+ ca R gim, lc axit gim.

+ Khi R c bn knh cng ha tr trung

gian v trng thi oxi ha (OXH) trung gian,hp cht c th hot ng nh mt axit hoc mt baz, tc l th hin tnh l ng tnh.


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i vi mt nguyn t ha hc c ccmc OXH khc nhau , lc axit tng khi s

oxi ha tng . V d lc axit ca dy Mn(OH) 2 Mn(OH) 7 tng .

G ii thch:+ Khi mc OXH tng, m in ca nguyn t tng hiu m in M O gim,

lin kt M OH tr thnh lin kt cng ha tr, phn cc O H tng, lc axit tng .

+ T Mn 2+ Mn+7 , mt in tch d ng trn Mn tng, kh nng y H+ tng, lm cholc axit tng .


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- i vi cc oxi ax it (HO) n EO m : Y u t quyt nh lc axit ca chng l m in

ca phi kim trung tm v s l ng nguyn t oxi (m) linkt vi E.+ i vi oxi axit c cng s m, lc axit tng theo m in ca E, m in ca E tng, lin kt O Hcng phn cc hn d phn ly ra H +.

V d: H2SO3: (HO)2SO v H2SeO3: (HO)2SeO. T S Se, m in gim (dc theo phn nhm), phn cc linkt E O (E: S,Se) tng, lin kt O H bn dn (km phncc hn), lc axit gim, pKa (H2SO3) = 1,87, pKa (H2SeO3) =2,62.

+ i vi cc oxi axit c s m khc nhau, lc axittng theo m. V nguyn t oxi c m in ln, n ht e ca E lm lin kt O H phn cc hn, cng d phn ly raH+.


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- Nu ion kim loi Mn+ c bn knh ln,in tch d ng nh + nh, kh nng y H+ kh nn t nh h ng n cc phn t n c b hirat ha; do hu nh khng c

lc axit (cation trung tnh (Na+

, K+

, Ca2+

...).- Nu ion kim loi Mn+ c bn knh nh,in tch d ng ln + ln, y H+ mnh nn th hin tnh axit (hay + ln nn htmnh oxi ca phn t n c hirat ha lmlin kt O H phn cc , kh nng tch H + d) l cc cation axit (Al 3+, Fe3+...).

c. Lc axit ca cc ion hirat ha


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+ Cc ax it c lc axit mnh hn H 3 O + Ta bit rng trong n c bt k axit no mnh hn H3O+ u chuyn hon ton proton cho baz n c to thnh H 3O+

khng mt axit no mnh hn H3O+ tn ti c trong n c .Vvy, khng th no xc nh c gi tr pKa ca chng.

V d: Trong n c khng th ni HCl hay HBr l mnh hn, v c hai thc cht phn ng hon ton vi n c to thnh H 3O+.

n c c hiu ng san bng mnh ca cc axit mnh, n lm cho tt c cc axit mnh u c lc axit ca axit H 3O + tc

l cc axit mnh u c mnh ngang nhau trong nc. Nicch khc, axit mnh nht trong nc l H 3O + Nh vy, i vi tt cc c ax it c pKa < 0 ta

khng th phn b it lc ca c hng trong dung

m i n c .

Phn bit lc axitbaz Bronstet trong dungmi n c

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- i vi cc axit yu c lc axit yu hn H 3O + nh ng mnh hn n c , ngha l 0 < pK a < 14. Cc axitny chuyn proton mt phn cho n c (phn ly mt phn trong n c ) nn trong dung dch tn ti phn t axit, ta c th xc nh c K a hay pK a ca chng,ngha l ta phn bit c mt cch nh l ng lc axitca chng.

- i vi cc axit yu hn H 2O tc l c pKa > 14

cng khng phn hng c bi v trong nc chngng vai tr l baz . xc nh lc axit ca chng(Ka) phi dng dung mi khc nc.

- Trong nc ch phn bit c lc axit ca

cc ax it c pKa t 0 14. 18

Cc axit c lc axit yu hn H 3 O +


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Tt c cc baz mnh hn OH - u khng tn ti c trong nc m phn ng hon ton vi nc to ra OH -. Vy, baz mnh nht c th tn ti trong nc l OH -. Nh vy, i v i tt cc c bazc pK b 14 tc l baz yu hn H

2O, ta cng khng xc nh

c lc baz v lc ny so vi nc th n li l axit. Mun xc

nh c lc baz phi dngdung mi khc nc.Kt lun : t rong nc ta ch

phn bit c mnh yu nhng axit hoc baz c 0 < pK a HBr > H2SO4 (nc 1) > HCl > HNO3

Trong dung mi khc nc

Cc dung mi m trong cc dung mi , s khcnhau v lc ca cc axit, hoc lc ca cc baz th hin mc ln, c gi l cc dung mi phn bit c. Ngc

li,

c

gi

l cc dung mi sanbng

. Khong phn bit lc axit baz ca dung mi c n nh bi chnh hng s

t phn li ca n . 21


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Hm axit, pH hiu dng v pKa quy i. Siuaxit

B + H + BH +

- Xt s proton ho mt baz yu trong mi trng axitmnh

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++ ++ +

+BB-1 HBH H

a a +a B BHH BH

H . . B .a a .a1K = = K = =

K a .a a BH .

+

+

B+H0

BH

.h = H . 0 0H = lghV

a 0 +

BK = h .

BH

a 0 +

BlgK = lgh + lg

BH

a 0 +

B pK = H lg

BH

0 a +

BH = pK + lg

BH hay


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- xc nh c H o ngi ta chn baz B m gi tr pK a (ca axit lin hp vi n, BH +) bit v sao cho bng thc nghim c th d dng xc nh c t s

H o c trng cho kh nng nhng proton ca mi trng, l c trng cho " axit" ca dung dch.

V th, ngi ta gi n l hm axit. H m axit ny xcnh c l nh dng cc baz ch th khng mang in tch nn gi l hm H o .

H o l mt i lng nhm m rng mc o nh

lng axi t, tc m rng thang pH , sang vng pH < 0.V th H o cn mang ngha l pH hiu dng .

[B]

[BH ]

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Gi tr H o ca H 2SO 4 100% l -12,1 chng t n

c kh nng cho proton rt mnh. Nu kh nng choproton ca mt mi trng no mnh hn H 2SO 4 100% tc l c H o < -12 chnh l nhng siu axit.

Cc mi trng siu axit nh dung dch SbF 5 hoc AsF 5 trong HSO 3F hoc trong HF c ng dng rng ri. Chng c dng to ra dung dch bn ca nhiu cacbocation, ion oxoni,cation axyl l nhng tiu phn tn ti rt t trong dungmi l axit thng thng. V d:

HH

F

SbF 5+HF

F

+

Hm axit, pH hiu dng v pKa quy i. Siu axi

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nh gi "nh lng baz" i vi mi trng baz mnh nh dung dch kim c, dung dch ca hiroxit tetrametylamoni, Me 4N+OH - trong DMSO v H 2O, ngi

ta dng cc axit yu m baz lin hp ca n mang in tchm lm ch th. V baz trong cn bng mang in tch m (-)nn hm axit thu c gi l hm H - ("ht tr'') . Th d:

p-O2N-C6H4-NH2 + OH- p-O2N-C6H4-NH- + H2ODMSO

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aB

K = h_ .HB

aB

pK = H_ lgHB

aB

H_ = pK + lgHB


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Nh vy, H l hm c trng cho kh nng nhn proton ca mi trng, tc c

trng cho " baz" ca mi trng. H lmt i lng dng m rng mc o nh lng " baz'' v pha pH > 14

Bng cch la chn cc h dung mi baz hoc dung mi axit thch hp, ngi ta thuc cc dung dch c khong Ho v H tri rng n cc gi tr -21 v +26. Tc l m rng thang o axit baz ca dung dch ngoi phm vi pH t 0 14. V vy, c i lng Ho v H c hiu l pH hiu dng .

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4-(O 2N)C 6H 4NH 2 (B1) l mt baz yu, axit lin hp ca n l 4-(O 2N)C 6H 4 H 3 c pKa c xc nh trong nc l0,99, cn i vi 2,4-(O 2N) 2C 6H 3NH 2 (B2) l mt baz rt yu, axit lin hp vi n l 2,4-(O 2N)2C 6H 3 H 3 c pKa < 0nn khng xc nh c trong nc.Ho tan ring B1 v B2 vo cng mt

mi trng axit mnh.

V d v tnh pKa quy i

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N

N


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T tnh c pK a ca 2,4-(O 2N) 2C 6H 3 H 3 trong nc l 4,53. Gi tr pKa = 4,53 c xc nh gin tip nh trn, do , n c hiu nh lgi tr pKa quy i v dung dch nc.

1

1

o 1a(B H )

[B ]pK H lg

[B H ]

2

2

o 2a(B H )

[B ]pK H lg

[B H ]

1 2

2 1

2 1a(B H ) a(B H ) [B ] [B ]pK pK lg lg[B H ] [B H ]

v

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Bit pK a ca 4-(O 2N)C 6H 4 H 3 trong nc l0,99. Nh phng php trc quang xc nh c gitr cc t s:

N

2

2[B ]

[B H ]

1

1[B ]

[B H ]

N


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i vi cc axit cc yu, nh cc axit loi C-H, N-H ngi ta cng ch c th c c gi tr pKa trong nc bng con ng gin tip nh s dng hm H- trong cc dung mi khcnc thch hp. Th d, i vi qu trnh gi

nh xy ra trong nc nh sau: 4-(O 2N)C 6H4NH2 4-(O 2N)C 6H4NH - + H +

S dng hm H -, ngi ta tnh c pKa = 18,4.30


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Tm li, bng cch la chn cc h dung mi axit hoc dung mi baz thch hp, s dng cc hm H o, H vi cc phng php thc nghim trc tip v tnh ton ngi ta thu c gi tr pKa trong nc cho mi axit, t cc yu nh axit cacbon (C H ), axit

nit (N H ) n cc mnh nh ccH X (tr H F ), H ClO 4 , H 2 SO 4 31


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Mi dung mi proton u c kh nng t phn li mc khc nhau.

Th d: i vi H 2O, NH 3 lng v HFlng: 2H2O H3O+ + OH

2HF H2F+ + F 2NH3 NH4+ + NH2

THUYT CC H DUNG MI

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V d: Trong amoniac lng, cc amiua ca kim loi nh NaNH 2, KNH 2, Ca(NH 2)2 l baz, cc mui amoni l axit. Ur cng laxit (mc d trong nc, n hon ton trung

tnh) 33

Ni dung thuyt cc h dung mi:- Axit l cht c th to ra trong dung

dch cation ng nht vi cation do dungmi t phn li ra.- Baz l cht c th to ra trong dung

dch anion ng nht vi anion do dungmi t phn li ra.


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Tnh cht ca cc baz tng t nhau * tan : LiOH t tan, NaOH, KOH... tan

LiNH2 t tan, NaNH2 tan t cn li u tan* Kh nng dn in: u l hp cht

ion, phn ly hon ton trong dung dch. * Dung dch baz lm qu tm ha

xanh, phenolphtalein khng mu chuyn

sang hng

2M + 2NH 3 2MNH 2 +H 2

2M + 2H2

O 2MOH + H2

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Phn ng to thnh baz t ng t nhau


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Phn ng to thnh axit t ng t nhau

Tnh cht ca cc axit tng t nhau * Tc dng vi baz to phn t dung mi

* Tc dng vi kim loi hot ng gii phng H 2

H2SO4+ 2H2O (H3O)2SO4

H2SO4 + 2NH3 (NH4)2SO4

H3O+ + OH 2H2ONH4+ + NH2 2NH3

Mg + (H3O)2SO4 MgSO4 + 2H2O + H2 Mg + (NH4)2SO4 MgSO4 + 2NH3 + H2

h h l h h h


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Zn(NH 2)2 + 2KNH 2 K 2[Zn(NH 2)4]Zn(NH 2)2 + 2NH 4Cl [Zn(NH 3)4]Cl2 Zn(OH) 2 + 2KOH K 2[Zn(OH) 4]

Zn(OH) 2 + 2[H 3O+]Cl2 [Zn(H 2O) 4]Cl2

Tnh cht l ng tnh ca cc cht t ng t nhauAl(OH)3, Zn(OH)2... tan c trong axit v

baz l cht l ng tnh. Al(NH2)3, Zn(NH2)2...tan c trong dung dch mui amoni v tan c trong dung dch mui amiua ca kim loi kim:

Tm li : Trong dung mi NH 3 lng, cc phn ng axit baz xy ra tng t nh trong nc. Dung mi NH 3 lng, HFlng, H 2O c gi l dung mi proton t ion ha.

M


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axi t baz

2BrF 3 2 4BrF BrF

2SO2

SO2+

+ 23

SO

SbBr 3 2SbBr Br

NOCl NO+

+ Cl

N 2 O 4 NO+

+3

NO

Mt s dung mi khng proton, t ion ha

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u im: Thuyt cc h dung mi xut pht t lun im t phn li ca dung mi nn cc khi nim axit, baz c m rng hn v thch hp hn.

- N p dng cho c dung mi proton v dungmi khng proton, do , c th ni thuyt proton ltrng hp ring nm trong thuyt cc h dung mi.

-ng thi, mt ln na cho php hiu ti saolc axit, baz khng phi l tnh cht tuyt i m ch

l tnh cht tng i ca cht tan. Ngha l cc lc ca cht tan th hin khc nhau trong cc dung mi

khc nhau.Thuyt h cc dung mi ngy cng c vai trquan trng i vi vic nghin cu phn ng axit baz trong dung mi khc nc.

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Nh c im: khng gii thch c phn ng trung ha xy ra trongiu kin khng c dung mi nh phn ng to thnh NH4Cl rn t khHCl v kh NH3 hay ch a gii thch c nguyn nhn lm cht ch th i mu khi tc dng vi cc axit, baz.

THUYT AXITBAZ CA LIUYT


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Ni dung:- Axit l tiu phn c kh nng nhn cp electron.- Baz l tiu phn c kh nng cho

cp electron to thnh lin kt chonhn .- T ng tc axit - baz l s to

thnh lin kt cng ho tr cho nhn , c tr ng cho s to thnh cc hp cht phc .

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THUYT AXIT BAZ CA LIUYT

B Li


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Baz Liuyt l nhng tiu phn c s

cho cp e-, chng c th l anion (OH

-, Cl

-,Br -...) hoc cc phn t trung ha m trong

phn t cn cp e- ch a tham gia lin kt (NH

3, amin,

hp cht

hu

c

ccha

oxinh r u , xeton...).

Nh vy nh ngha baz ca Liuytkhng m rng khi nim baz v theoBronstet - Laury, tiu phn l baz khi nc kh nng nhn proton, tc l cng phi c cp e- cho i.

Baz Liuyt

A i Li


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Axit l nhng tiu phn c d mt in tch d ng hoc l nhng phn t (hoc ion) cn c cc obitantrng thch hp cho vic nhn e t baz chuyn sang. c th l H+,HCl hoc BF3, Cu2+, Cr 3+...(khng cha hiro trong cng thc nn khng th l axit protonic). iu cng cngha l, tt c cc axit Bronstet Laury u l axit Liuyt.

Axit Liuyt

Phn ng axit baz theo Liuyt


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1. Phn ng cng : Sn phm ca bt k

phn ng axit baz Liuyt no cng c gi l sn phm cng (adduct), i khi cn gi l phc cht

A : B A - B (sn phm cng hp)

S d to ra sn phm cng bn l do obitan lin kt mi c nng lng thp hn c hnh thnh v c lp y

bi cc cp electron t HOMO ca baz nn h thp nng lng ca h.

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Phn ng axit baz theo Liuyt

C nhng h t hot ng a nh mt i li a nh


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C nhng phn t hot ng va nh mt axit li va nh mt baz Liuyt v nhng phn t va c nguyn t c kh nng nhn cp electron va c nguyn t c kh nng cho cp electron. Th d, SnCl

2 th hin ln lt nh mt axit, ri nh mt

baz trong cc phn ng sau:

SnCl 2 24PtClCl 3

3 3 5SnCl Pt(SnCl )

3 3 3

3 3 3N(CH ) BF

2 2 3 3

F B N(CH )\ /

SnCl Cl SnN(CH ) Sn

/ \Cl Cl

Axit l cht nhn electron nn cn c gi l cht electrophin, cn baz l cht choelectron hoc cht nucleophin 44


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Phn ng th mt axit hoc baz Liuyt ny bng mt axit hoc baz Liuyt khc:

B - A + :B' :B + A-B'

(C2H5)2O-BF3 + :NC5H5 (C2H5)2O + F3B-NC5H5

A + B - A' B - A + A'

BF3 + C5H5N-SnCl2 C5H5N-BF3 + SnCl2 Phn ng trao i

A-B + A-B ' A-B' + A-B

(C2H5)3Si - I + AgBr (C2H5)3Si-Br + AgI

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2. Phn ng th

Mts axit Liuyt th ng gp


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Axit L iuyt cha nguyn t thiu ht electron laxit cha nguyn t trung tm cha 8 electron :

- Cc hp cht cng ho tr ca cc nguyn t nhm IIIAnh cc halogenua ca B, Al, Ga, In, v Tl.

- Cc halogenua ca Si, Ge, Sn, Pb, P, As, Sb, Bi trng thi oxi ho thp nh SnCl 2, AsCl 3, BiCl 3

Nhng hp cht ny phn ng rt mnh honchnh bt t .

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Mt s axit Liuyt th ng gp


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l i


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Ax it Liuyt l ion k im loi

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HH

BASE

Co2+

CID

O HO H

Co2+


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Phn ng ca NH3 vi Cu2+


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- Tnh l ng tnh ca Al(OH) 3(s)

c gii thch nh sau: Al(OH) 3(s) + 3H + Al3+ + 3 H 2O y Al(OH) 3 l baz theo

Bronstet Al(OH) 3(s) + OH - Al(OH) 4- y Al(OH)3 l axit liuyt

Al :O-H- 50

LCAXIT BAZLIUYT


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d on nh tnh lc axit - baz Liuyt ng i ta cn c vo yu t cm ng , cng hng v lp th: Hiu ng ht, y electron ca

nhm th n in tch d ng trnnguyn t c kh nng nhn e - vin tch m trn nguyn t c cp e - ch a tham gia lin kt. Lin kt c d hay kh b ph v khitham gia phn ng . Hiu ng khng gian.

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LC AXIT BAZ LIUYT

BF BCl BB t i phi h


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BF 3 - BCl 3 - BBr 3: t tri sang phi tnhaxit tng dn:

iu ny khng ph hp vi qui lut da trnhiu ng cm ng. y gii thch lc axit tng dn ta da trn kh nng ph v lin kt d hay kh.Trong phn t BF 3, nguyn t B trng thi lai hasp 2. Phn t gm 3 lin kt v 1 lin kt cho nhn (t F n B) khng nh v, gii ta u 4 tm nn BF 3 khng c obitan trng. Khi tc dng vi mt baz Liuyt th BF 3 phi chuyn t dng lai ha sp 2 thnhlai ha sp 3 xen ph to lin kt cng ha tr cho -nhn vi baz Liuyt , v vy lin kt b ph v .

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ca phn ng gia piriin


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ca phn ng gia piriin,metylpiriin vi B(CH3)3 ln l t l:

71 74 42 (kJ)Cn tr khng gian lm 2-metylpiriin c tnh baz yu hn so vi

piriin v 3-metyl piriin (gi tr ca phn ng b nht)53

N

B(CH 3 ) 3

N

B(CH 3 ) 3

CH 3

N

B(CH 3 ) 3CH 3

Nh vy em t lc a it baz Li t phi em t


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Nh vy , xem xt lc axit - baz Liuyt phi xem xty nh h ng ca tt c cc yu t cm ng , cng h ng v lp th . iu ny rt kh khn v phc tp ,

c nhng tr ng hp khng gii thch c :Kh nng to phc ca ion halogenua vi Al3+ tng dn theo trt t I- < Br< Cl < F nh ng i vi Hg2+ th ng c li I- > Br - > Cl- > F-

Nhit ca phn ng gia I2 v (C2H5)2S ln hn vi (C2H5)2O nh ng nhit ca phn ng gia C6H5OHvi (C2H5)2S li nh hn vi (C2H5)2O. gii thch s khc bit ny, nm 1963 Pearson a ra qui tc axit baz cng mm da vo bn ca cht to thnh.

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Axit hoc baz mm l axit hoc baz m e - ha tr


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Axit hoc baz mm l axit hoc baz m e ha tr ca chng d b phn cc ha, d hnh thnh lin kt cng ha tr (+ nh - - nh) (d b phn cc ha i

vi baz mm cng l d cho cp e-)

Axit hoc baz cng l axit hoc baz m e - ca chng b gi cht, kh bin dng, t ng tc gia chng ging nh t ng tc ion (+ ln - ln).

Nh vy, cc axit baz cng kh bin dng tnhaxit baz ca chng cng cng , cc axit baz d b bin dng th tnh axit baz ca chng cngmm. Tnh cht cng hay mm ca cc axit baz gn lin vi kh nng b phn cc ca chng, do c lin quan trc tip n cu to lp v e-, kchth c v in tch ca chng.

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Quy tc Pearson:


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i vi tng tc cng - cng, lc ht Culong c tcdng quan trng, cn i vi tng tc mm - mm thphn ng gp ca lin kt cng ho tr l quan trng hn.

Q yAxit cng a bazcng, axit m m a bazm m .

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Al3+ l axit cng, n d dng lin kt vi baz

cng nh

F-, cn Hg 2+ l axitmm

, nd

dng linkt

vi

baz mm nh I-. V t I- n F- bn knh gim, - tng, F- tb bin dng d i tc dng ca cation hn I-.

V bn knh ca oxi nh hn bn knh ca l u hunh nn - trn oxi ln hn trn S, dn n kh nng b phn cc ca (C2H5)2O km hn so vi (C2H5)2S nn(C2H5)2S l baz mm, I2 li l axit mm nn nhit ca phn ng ta ra mnh, phn ng rt thun li. CnC6H5OH l axit cng nn phn ng mnh vi baz cng l

(C2H5)2O.

S h hi i b h h g h


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- S phn chia axit, baz thnh cng hay mm khng phi l tuyt i v cng khng phi l c mt ranh gii r rt. Ni chung tnh cng ca axit baz lion n gin th gim dc theo nhm, th d:

Li+ > Na+ > K+;Zn2+ > Cd2+ > Hg2+;F-> Cl- > Br - > I-.- i vi cc baz l cc tiu phn ng

electron (isoelectron) th tnh cng tng dc theo chuk : NH 2- < OH < F .

- tnh cng ca nguyn t thng tng theos tng trng thi oxi ho. i t u nhm n cui nhm th tnh cng gim i vi cc hp cht ccng s oxi ho ca nguyn t trung tm.

57


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58

u im: Thuyt electron ca Liuyt m rng rt nhiu so vi cc thuyt axit - baz tr c . Thuyt ca Liuyt gii thch c , m rng c nhng hn ch ca thuyt Bronstet - Laury v phn ng axit -baz ch c s trao i proton. Liuyt cho rng tt c cc phn ng tr phn ng thc cht c s cho v

nhn hn e-

u l phn ng axit - baz . Nhc im: Hn ch ln nht ca thuyt lkhng gii quyt c mt cch tha ng vic nh l ng lc ca axit - baz nh thuyt ca Areniuyts vthuyt ca Bronstet - Laury.

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