GREEN CHEMISTRY

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GREEN CHEMISTRY

Laurea Magistrale in Scienze Chimiche Prof. Leucio Rossi 6 CFU – AA 2017-2018

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SOLVENTS IN GREEN CHEMISTRY III

Green Chemistry 07

Green Chemistry – Prof. Rossi – AA 2013-2014

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Solvents in Green Chemistry

Use safer solvents and auxiliaries

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FLUOROUS SOLVENTS AND RELATED SYSTEMS

INTRODUCTION

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Introduction

• Highly fluorinated materials, are not soluble in common laboratory (VOC) solvents.

• Fluorinated materials such as Teflon^TM are very unreactive.

• Horvath and Rabai in 1994,report the use of these materials as solvents in catalysis and separations (Fluorous Biphase System)

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Properties

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Introduction

BTF (boiling point 102°C, mel;ng point −29°C)

F-626 (boiling point 214°C, glass transi;on −110°C)

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Introduction

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Introduction

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Introduction

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Introduction

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Introduction

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Properties

Polarity

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Properties

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Proper&es

The fluorous approach takes advantage of the low solubility of fluorinated molecules in

common VOC- based solvents and also their inherent lack of reactivity. Horvath coined the term fluorous biphase system (FBS) to describe these systems. Just as in water-organic

separations, where one has an aqueous phase and an organic phase, if a highly fluorinated solvent is used, e.g. perfluorocyclohexane, a

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Properties

In addition to their separation properties,

perfluorocarbons have the following advantages as solvents: they are chemically unreactive,

nonflammable and have a low toxicity. But their low reactivity leads to long lifetimes and as

these solvents are still volatile, there is a high chance that atmospheric contamination will occur.

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Properties

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Proper&es

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Properties

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Properties

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Properties

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Proper&es

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Toxicity and environmental issues

• Saturated perfluorocarbons present few if any toxicity problems, and extensive use is made of them in household cookware;

• No saturated perfluorocarbon has been found to contribute in any way to ozone depletion;

• Environmental half-lives have been

estimated as 4.1 × 10³ years for C₅F₁₂ and 3.1

× 10³ years for C₆F₁₂.

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FBS

The FBS approach has now been used in many different ways, including the following:

1. Traditional FBS (separation by liquid–liquid extraction)

2. Amphiphilic-solvent approach (separation by filtration after the reaction). An amphiphilic solvent (e.g. α, α, α-trifluorotoluene,

CF₃C₆H₅) may provide an appropriate solubility for both the fluorous and the organic materials and the reaction can proceed in a

homogeneous fashion with a single solvent. After the reaction is complete, an organic solvent can be added to precipitate the fluorous material.

3. Fluorous reverse–phase silica gel (separation by solid-phase extraction).

The hydroxyl residues on silica gel are modified with perfluoroalkyl chains. This causes a fluorophilic effect between the fluorous

reagent, catalyst or product and allows facile separation independent of temperature.

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FBS

4. Triphasic reactions. For example, fluorous–organic–

aqueous phases or two organic phases separated by a fluorous phase in a U-tube reaction flask.

5. Fluorous biphasic catalysis without fluorous solvents (filtration of a thermomorphic fluorous catalyst). This can be used when a fluorous catalyst exhibits significantly

different solubility in an organic solvent upon changing the temperature of the system.

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Fluorous Catalysts and Reagents

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Fluorous Catalysts and Reagents

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Fluorous Catalysts and Reagents

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Fluorous Extractions

the extraction of photodegraded solid and liquid wastes contaminated with polychlorinated biphenyls (PCBs).

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Fluorous Reactions

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Fluorous Reactions

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Fluorous Reac+ons

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Fluorous Biphase Catalysis

In 1994,

• Horváth and Rabai reported the first fluorous biphase cataly@c system. They studied hydroformyla@on of olefins and demonstrated the extrac@on of their rhodium catalyst, which contained the trialkyl

phosphine P(CH₂CH₂C₆F₁₃)₃, from the organic toluene phase.

There have been many equally elegant studies in this ﬁeld since this ini@al

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report. Cataly@c reac@ons that have been studied to date under FBS condi@ons include hydrogena@ons, hydrobora@ons, hydrosila@ons, C–C bond forma@ons and oxida@ons of sulﬁdes, alkenes, alkanes and

aldehydes.

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

Hydroformylation

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Fluorous Biphase Catalysis

Hydrogena4on

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Fluorous Biphase Catalysis

hydrosilation

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Fluorous Biphase Catalysis

Catalytic hydroboration

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Fluorous Biphase Catalysis

Catalytic oxidation reactions

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Fluorous Biphase Catalysis

Cataly0c oxida0on reac0ons

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

Coupling reactions

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Fluorous Biphase Catalysis

Coupling reac3ons

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

Fluorous acid and base catalysts

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

Enantioselective Reduction

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Fluorous Biphase Catalysis

Enan2oselec2ve Epoxyda2on

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Fluorous Biphase Catalysis

Et₂Zn or Et₃Al addition to aldehydes

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Fluorous Biphase Catalysis

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Fluorous Biphase Catalysis

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Heavy Fluorous Reagents

Fluorous 0n hydrides

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Heavy Fluorous Reagents

The Stille coupling reaction

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Heavy Fluorous Reagents

Radical carbonylation reaction

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Heavy Fluorous Reagents

Fluorous sulfide and sulfoxide

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Heavy Fluorous Protecting Groups

When reagents or products contain >60% by weight

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of ﬂuorine atoms, they generally parBBon into

ﬂuorous solvents upon separaBon via ﬂuorous and organic liquid/liquid extracBon.

When the ﬂuorous content is much lower than 60%

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(light ﬂuorous molecules), more eﬀecBve

separaBon must be used, such as solid-phase extracBon with reverse-phase silica gel

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Heavy Fluorous Protecting Groups

Trifluoroalkylsilyl protecting group

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Heavy Fluorous Protec/ng Groups

Fluorous alcohol protective group

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Heavy and Light Fluorous Molecules

Heavy fluorous techniques use fluorous reaction components that have a large number of fluorines.

Heavy fluorous molecules can have as few as ^∼39 fluorines, but it is not uncommon for them to have

>50 or even >100. Such a high fluorine content gives heavy fluorous molecules unusual

properties, and they can be separated from

reaction mixtures by simple separation techniques such as extraction with a fluorinated solvent or

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Heavy and Light Fluorous Molecules

Light fluorous molecules typically have 21 fluorines or fewer, and par>>on coefficients are o@en too low for efficient extrac>on into fluorinated

solvents. However, such molecules can be

separated from organic molecules by a ﬂuorous solid-phase extrac>on and from each other as well as organic molecules by ﬂuorous chromatography.

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Solid-phase extractions

fluorous silica gel,

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Light Fluorous Reagents

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Light Fluorous Catalysts

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Light Fluorous Scavengers

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Light Fluorous Protecting Group

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Fluorous Reac+ons in scCO ₂

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GREEN CHEMISTRY

GREEN CHEMISTRY

SOLVENTS IN GREEN CHEMISTRY III

Solvents in Green Chemistry

Use safer solvents and auxiliaries

FLUOROUS SOLVENTS AND RELATED SYSTEMS

Introduction

Properties

Introduction

Introduction

Introduction

Introduction

Introduction

Introduction

Properties

Polarity

Properties

Proper&es

Properties

Properties

Proper&es

Properties

Properties

Properties

Proper&es

Toxicity and environmental issues

FBS

FBS

Fluorous Catalysts and Reagents

Fluorous Catalysts and Reagents

Fluorous Catalysts and Reagents

Fluorous Extractions

Fluorous Reactions

Fluorous Reactions

Fluorous Reac+ons

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Fluorous Biphase Catalysis

Heavy Fluorous Reagents

Heavy Fluorous Reagents

Heavy Fluorous Reagents

Heavy Fluorous Reagents

Heavy Fluorous Protecting Groups

Heavy Fluorous Protecting Groups

Heavy Fluorous Protec/ng Groups

Heavy and Light Fluorous Molecules

Heavy and Light Fluorous Molecules

Solid-phase extractions

Light Fluorous Reagents

Light Fluorous Catalysts

Light Fluorous Scavengers

Light Fluorous Protecting Group

Fluorous Reac+ons in scCO 2

Fluorous Triphasic Reactions

Fluorous Reac+ons in scCO ₂