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Changes in Solvolysis Mechanisms:

From Classical S

N

1 Reactions

to Persistent Ion Conditions

Dipl. Chem. Heike Schaller

aus

Bremen

München, 2008

Diese Dissertation wurde im Sinne von § 13 Abs. 3 der Promotionsordnung vom 29. Januar 1998 von Herrn Prof. Dr. Herbert

Mayr betreut.

erarbeitet.

München, 04.09.2008

Heike F. Schaller

Dissertation eingereicht am 04.09.2008

1. Gutachter Prof. Dr. Herbert Mayr

2. Gutachter Prof. Dr. Hans Rudolf Pfaendler

Mündliche Prüfung am 15.10.2008

Für

meine Eltern & Olli

Danksagung

Mein besonderer Dank gilt Herrn Prof. Dr. Herbert Mayr für die Überlassung des interessanten Themas, seiner Diskussionsbereitschaft Bereitstellung der hervorragenden experimentellen Bedingungen.

Arbeitsklima und die tolle Zusammenarbeit danken.

Mein besonderer Dank gilt meinen aktuellen und ehemaligen Kollegen der Chemie. Herrn Prof. Dr. Eberhard Riedle und besonders Uli Schmidhammer sei für die gute Zusammenarbeit bei unserem Cyanat-Projekt gedankt. Frau Prof. Dr. Cinzia Chiappe danke ich für die Zeit, die ich in ihre r Arbeitsgruppe in Pisa forschen durfte und ihren Mitarbeitern, insbesondere freundliche Aufnahme. Für die schnelle und kritische Durchsicht dieser Arbeit sei Oliver Kaumanns, Martin Breugst, Patrick Kaumanns, Nicolas Streidl, Roland

Appel und Dorothea Richter gedankt.

Meinen Eltern und meinem Freund danke ich vor allem für die

Publikationen

Direct Observation of the Ionization Step in Solvolysis Reactions: Electrophilicity versus Electrofugality of Carbocations H. F. Schaller, A. A. Tishkov, X. Feng, H. Mayr, J. Am. Chem. Soc. 2008, 130, 3012- 3022.
"Carbokationen-Watching" bei Solvolyse-Reaktionen "Carbocation Watching" in Solvolysis Reactions H. F. Schaller, H. Mayr, Angew. Chem. 2008, 120, 4022-4025; Angew. Chem. Int. Ed.

2008, 47, 3958-3961.

Ambident Reactivity of the Cyanate Anion

H. F. Schaller, U. Schmidhammer, E. Riedle, H. Mayr, Chem. Eur. J. 2008, 14, 3866- 3868.

Konferenzbeitrag

Direct Observation of Intermediate Carbocations in Solvolysis Reactions

List of Abbreviations

A acetone

abs. absolute

AN acetonitrile

aq. aqueous

Bu butyl

calc. calculated cf. confer conc. concentrated d doublet

E electrophilicity parameter

E ethanol

EA elementary analysis

Et ethyl

EtOAc ethyl acetate

eq. equivalent(s) exp. experimental h hour(s) i.e. id est i. vac. in vacuo k rate constant lit. literature

M mol/L

M methanol

Me methyl

min minute(s) mp melting point

MS mass spectrometry

N nucleophilicity parameter

NMR nuclear megnetic resonance

Ph phenyl

q quartet

Rf retention factor

s nucleophile specific slope parameter s singlet t triplet

UV ultra violett

Vis visible

vs. versus

W Water

Table of Contents

0 Summary 1

1 Introduction 13

2 Direct Observation of the Ionization Step in Solvolysis 16

Reactions: Electrophilicity versus Electrofugality of Carbocations

Introduction 16

Results and Discussion 20

Conclusion 44

References 45

Experimental Section 48

Appendix 97

3 "Carbocation Watching" in Solvolysis Reactions 111

Introduction 111

Results and Discussion 112

Conclusion 118

References 119

Experimental Section 121

4 Nucleofugality of Common Leaving Groups in Solvolysis 134

Reactions: An Extension of the Nucleofugality Scale

Introduction 134

Results and Discussion 135

Conclusion 155

References 155

Experimental Section 158

5 Ambident Reactivity of the Cyanate Anion 182

Introduction 182

Results and Discussion 183

Conclusion 187

References 187

Experimental Section 189

Chapter 0: Summary

Summary

Nucleophilicity of Carboxylates

Rates and equilibria of the reactions of highl

y stabilized amino-substituted benzhydrylium ions (Ar 2 CH

1, -5 > E > -10) with carboxylate ions (RCO

2

2: acetate AcO

, benzoate BzO , p- nitrobenzoate PNB and 3,5-dinitrobenzoate DNB ) have been determined photometrically in

acetone and acetonitrile solutions. Scheme 0.1. Reactions of Benzhydrylium Ions 1 with Carboxylates 2 at 25 °C.

ArArO O R ArAr O O R k-1

25 °C

H 12 3 Me O O O O OO O 2 N O O O 2 N O 2 N AcO BzO PNB DNB

Table 0.1. Employed Benzhydrylium Ions Ar

2 CH and Their Electrophilicity Parameters E. H XY+ Ar 2 CH X Y E (ani) 2 CH OCH 3 OCH 3 0.00 (fur)(ani)CH HOO -0.56 (dma)(Ph)CH N(CH 3 2 H - a (fur) 2 CH HOO -1.36 (pfa) 2 CH

N(Ph)CH

2 CF 3

N(Ph)CH

2 CF 3 -3.14 1

Chapter 0: Summary

Table 0.1. Continued.

H XY Ar 2 CH X Y E (mfa) 2 CH N(CH 3 )CH 2 CF 3 N(CH 3 )CH 2 CF 3 -3.85 (dpa) 2 CH NPh 2 NPh 2 -4.72 (mor) 2 CH H NN OO -5.53 (mpa) 2 CH

N(Ph)CH

3

N(Ph)CH

3 -5.89 (dma) 2 CH N(CH 3 2 N(CH 3 2 -7.02 (pyr) 2 CH N(CH 2 4 N(CH 2 4 -7.69 (thq) 2 CH H N Me MeN -8.22 (ind) 2 CH H N Me MeN -8.76 (jul) 2 CH H NN -9.45 (lil) 2 CH H NN -10.04 a not determined. Plots of the logarithmic second-order rate constants log k -1 of the reactions of benzhydrylium ions 1 with carboxylates 2 vs. the electrophilicity parameter E resulted in linear correlations (Figure 0.1). 2468
-12 -10 -8-6-4-2 PNB -/A A cO -/AN BzO -/AN P NB -/AND NB/A D NB -/AN A cO -/10W90A BzO -/10W90AN

Electrophilicity Elog k

-1 (jul) 2 CH (mpa) 2 CH (dpa) 2 CH (mor) 2 CH (pfa) 2 CH (lil) 2 CH (thq) 2 CH Figure 0.1. Correlations of the second-order rate constants k -1 (25 °C) for the combination of benzhydrylium ions 1 with carboxylate ions 2 in different solvents. A = acetone, AN = acetonitrile,

W = water.

2

Chapter 0: Summary

The obtained second-order rate constants k

-1 (Scheme 0.1) have been employed to determine the

nucleophilicity parameters s and N of the carboxylate ions at 25 °C, according to the linear free-

energy relationship 0.1. log k = s(N + E) (0.1) In this equation, the electrophiles are characterized by the electrophilicity parameter E and nucleophiles are characterized by a nucleophilicity parameter N and a nucleophile-specific slope- parameter s.

1113151719

N AcO

10W90AN

AcO

20W80ANBzO

20W80ANBzO

10W90ANAcO

10W90AAcO

20W80ADNB

ANPNB ANBzO ANAcO ANPNB ADNB A Figure 0.2. Comparison of the nucleophilicity parameters N of the carboxylates 2 in different solvents at 25 °C. The nucleophilicity parameters N of the carboxylates are in the range of 13 > N > 10 for aqueous solvents, and in the range of 19 > N > 14 for pure acetone and acetonitrile. Direct Observation of the Ionization Step in Solvolysis Reactions of

Benzhydrylium Carboxylates

Kinetics of the ionization of benzhydryl carboxylates (Ar 2 CH-O 2

CR 3) have been studied

photometrically (formation of the colored amino-substituted benzhydrylium ions Ar 2 CH

1 -6 > E >

-10) by adding water to the colorless solutions of Ar 2 CH-O 2

CR 3 in acetone or acetonitrile.

3

Chapter 0: Summary

Scheme 0.2.

Ionization of Benzhydrylium Carboxylates 3 in Aqueous Acetone and Acetonitrile

Mixtures at 25 °C.

ArArO O RArAr O O RH k 1 3124
ArAr OH H 2 Oquotesdbs_dbs17.pdfusesText_23