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  3. Green preparation of acylals and acetates from aldehydes and alcohols in solvent-free conditions

Green preparation of acylals and acetates from aldehydes and alcohols in solvent-free conditions

Number of pages: 103 File Format: word File Code: 31898
Year: 2011 University Degree: Master's degree Category: Chemical - Petrochemical Engineering
Tags/Keywords: Acetate - Aldehyde - aromatic - Carbonyl - functional groups - green asilal - Multi-agent combinations - Protection of carbonyl groups - Stall
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  • Summary of Green preparation of acylals and acetates from aldehydes and alcohols in solvent-free conditions

    Dissertation for Master's Degree in Organic Chemistry

    Abstract

    Protection and deprotection of functional groups is one of the inevitable steps in the synthesis of multi-functional compounds. Selective protection of carbonyl groups is very important in modern organic chemistry. 1-Diacetates are one of the basic protective groups of the carbonyl functional group due to their stability in neutral, basic and acidic environments. On the other hand, the development and application of environmentally friendly catalysts and solvents and the advantages of solvent-free reactions such as high reaction speed, easy purification, reduction of pollution, high product efficiency and low cost are important and significant topics in organic chemistry. In this treatise, new and improved methods for the synthesis of acylals from aldehydes are introduced by the following systems:

    - Aldehydes/Ac2O/H2SO4 system supported on charcoal in solvent-free and room temperature conditions.

    - Aldehydes/Ac2O/H3BO3 system in solvent-free and oil bath conditions.

    In addition, the protection of hydroxy alcohols and phenols groups by ester formation is also one of the most important and widely used transformations in organic chemistry. Protection of such functional groups during various transformations in a synthetic sequence is often necessary, especially in the preparation of multi-functional molecules. In this treatise, simple and effective methods for protecting alcohols in the form of acetylation by the following systems have been investigated:

    - Alcohols/Ac2O/H2SO4 system supported on charcoal in solvent-free and room temperature conditions.

    - Alcohols/Ac2O/Mo powder system in solvent-free and oil bath conditions.

    Chapter First

    Introduction

    1-1- Protection

    The protection of functional groups is of special importance in organic chemistry. Protecting groups play a key role in synthetic chemistry, especially in multi-step syntheses. 1-4 When the goal is to synthesize a relatively complex molecule, a series of reactions leading to the expected product must be designed. Currently, there are syntheses that require fifteen to twenty steps. In the design and execution of such multi-step syntheses, the noteworthy point is that the functional groups that are already present in the molecule compete with the reaction conditions required for the next steps. Sometimes it is necessary to change a functional group in order to avoid interference with some reactions in the synthetic sequence. A protecting group can be placed in place and then subsequently removed to prevent an unwanted reaction or other adverse effect. In choosing a suitable protecting group, one should pay attention to several important points:

    1- The nature of the group to be protected.

    2- The reaction conditions under which the conditions of the protecting group are stable.

    3- The conditions that can be provided to remove the protecting group.

    No type of comprehensive protecting group and There is no inclusiveness. However, this method has been upgraded to high levels and provides many protecting groups for the synthesis of complex molecules. Fortunately, the methods of adding and removing protective groups have been fully developed and the efficiencies are usually excellent. One of the characteristic features of the carbonyl group is its electrophilicity, which must be protected against the attack of various reagents such as nucleophiles during the various stages of multi-step synthesis, which include acidic, basic, organometallic reagents, or reducing and oxidizing agents.8-5

    1-1-2-Acetals

    A very general way to protect aldehydes and ketones against increasing or decreasing nucleophilicity is to convert them into acetals. 9 For this purpose, ethylene glycol is often used, which creates a cyclic dioxalane derivative. Dioxalanes are usually prepared by heating a carbonylated compound with ethylene glycol in the presence of an acid catalyst, and the necessary provision must be made for the azeotropic removal of water (reaction 1-1). Various heterogeneities have been reported. Among the homogeneous catalysts, we can mention triflic acid, paratoluenesulfonic acid (PTSA) and pyridinium salts. 10-13

    Among the various heterogeneous catalysts, metal sulfates supported on silica gel can be mentioned (reaction 1-2). 14

    reaction (1-2)

    In one case, zirconium sulfonyl phosphonate [[Zr(CH3PO3)1.2(O3PC6H4SO3H)0.8] was used to prepare acetals (reaction 1-3). 15

    Reaction (1-3)

    In another case, to protect ketones from the catalyst ZrO2 / SO42- has been reported (reaction 1-4). 16

    Another carbonyl protector is the 1,3-oxathiolane derivative, which can be prepared by reacting with mercaptoethanol in the presence of a number of Lewis acids including BF317 and In(OTf)318 or heating with a catalyst. Acidity was prepared while azeotropically extracting its water. 19 3-Oxathiolans are especially useful and applicable when deprotection is required in non-acidic conditions. In the following reaction, kaolin is used to prepare 1,3-oxathiolane derivative (reaction 1-5). 20

    Reaction (1-5)

    Dithioacetals are also useful for protecting carbonyl groups. 21 These groups can be prepared from the reaction of dithiols in the presence of Lewis acid catalysts. For example, in one case, tungstophosphoric acid (H3PW12O40) has been used as a heterogeneous catalyst for thioacetylation of aldehydes and ketones, reaction (1-6). In this mechanism, first a hemistal is formed and then the corresponding estal is created (Shamai 1-1). 23

    Shamai (1-1)

    But Granwald showed in a study that the steps shown above for the formation of hemiastal are simultaneous (reaction 1-7). 24

    Reaction (1-7)

    1-1-3- Acylals (1-1-diacetates)

    In recent years, acylals (1-1-diacetates) have received much attention as a good protector for aldehydes and have replaced acetals. 1 The reason for the superiority of acylals over acetals is that acylals are stable in mild acidic, neutral and alkaline environments, and they are easy to prepare. 25 In addition, another advantage of acylals compared to acetals is this. which, during the reaction of acetal formation, water is produced, which must be removed by physical or chemical methods, while, during the formation of acylals, such an action is not necessary. Another important point is the chemoselective synthesis of 1-1-diacetes from aldehydes in the presence of ketones, so that the ketone in the environment does not react even at high temperatures and for long periods of time. rtl;">Acylals obtained from aliphatic aldehydes in the presence of KCN and in DMSO solvent create cyanohydrin esters with excellent efficiency at room temperature

     

    ABSTRACT

    Protection and deportation of functional groups are indispensable ingredients of the synthesis of polyfunctional compounds. Selective protection of carbonyl groups is extremely important in modern organic chemistry.

  • Contents & References of Green preparation of acylals and acetates from aldehydes and alcohols in solvent-free conditions

    List:

    Chapter One: Introduction

    1-1- Protection. 1

    1-1-1- Protection of carbonyl groups. 1

    1-1-2- Acetals 1

    1-1-3- Acylals (1-1-diacetates) 4

    1-1-4- Uses of acylals 4

    1-1-5- Preparation methods of acylals 8

    1-1-6- Investigating the formation mechanism of 1-1-diacetates 10

    1-1-7- Synthesis of 1- and 1- diacetates from non-aldehyde compounds. 11

    1-2- Protection of alcoholic groups. 13

    1-2-1- ether protection of alcohols 13

    1-2-2- ester protection. 15

    1-3- The use of green conditions in discontinuous processes of producing chemical products. 16

    1-3-1- organic syntheses without solvent using reagents or inorganic catalytic media and microwave. 16

    1-3-2- organic syntheses using ionic liquids. 18

    Aim of the present research work 19

    Chapter Two: Experimental part

    2-1- Generalities. 20

    2-2- A sample laboratory procedure for converting aldehydes into 1- and 1-diacetates using sulfuric acid placed on activated charcoal under solvent-free conditions. 20

    3-2-Example of the laboratory procedure for converting aldehydes to 1- and 1-diacetates using H3BO3 under solvent-free conditions and oil bath 21

    2-4-Example of the laboratory procedure for converting alcohols to the corresponding esters using sulfuric acid placed on activated charcoal under solvent-free conditions. 21

    2-5-Example of a laboratory procedure for converting alcohols to the corresponding esters using metallic molybdenum under solvent-free and oil-bath conditions 22

    Chapter three: discussion and conclusions

    3-1- Synthesis of acylals (1- and 1-diacetates) from aldehydes using sulfuric acid system placed on activated charcoal under solvent-free conditions at room temperature. 23

    3-2- Synthesis of 1 and 1- diacetates from the corresponding aldehydes by H3BO3 under conditions without solvent and oil bath. 28

    3-3- Synthesis of acetates from related alcohols using sulfuric acid system placed on activated charcoal under solvent-free conditions and room temperature 31

    3-4- Synthesis of acetates from related alcohols using Mo metal under solvent-free conditions and oil bath. 37

    Chapter Four: Spectrums and sources

    Appendix of spectra 42

    Resources

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Green preparation of acylals and acetates from aldehydes and alcohols in solvent-free conditions
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