Atherton–Todd reaction | |
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Named after | Frank R. Atherton Alexander R. Todd |
Reaction type | Substitution reaction |
Identifiers | |
RSC ontology ID | RXNO:0000690 |
The Atherton-Todd reaction is a name reaction in organic chemistry, which goes back to the British chemists F. R. Atherton, H. T. Openshaw and A. R. Todd. These described the reaction for the first time in 1945 as a method of converting dialkyl phosphites into dialkyl chlorophosphates. [1] The dialkyl chlorophosphates formed are often too reactive to be isolated, though. For this reason, the synthesis of phosphates or phosphoramidates can follow the Atherton-Todd reaction in the presence of alcohols or amines. The following equation gives an overview over the Atherton-Todd reaction using the reactant dimethyl phosphite as an example:
The reaction takes place after the addition of tetrachloromethane and a base. This base is usually a primary, secondary or tertiary amine. Instead of methyl groups other alkyl or benzyl groups may be present.
A possible reaction mechanism for the Atherton-Todd reaction is presented here for the example of dimethylphosphite, just like in the overview reaction: [2]
First, a tertiary amine is used to cleave a methyl group of dimethyl phosphite. The intermediate 1 results from this reaction step.
Subsequently, the intermediate 1 deprotonates the starting compound dimethylphosphite, so that intermediates 2a and intermediates 2b are formed. The intermediate 1 is then regenerated from the intermediate 2a.
Finally, intermediate 2b is chlorinated by tetrachloromethane and dimethyl chlorophosphate 3 is formed.
After the synthesis of the dimethyl chlorophosphate, a further reaction (for example with a primary amine like aniline) is possible by the following reaction equation: [3]
In this reaction, in addition to the starting compound dialkyl phosphite, tetrachloromethane and a base (an amine) are used in stoichiometric amounts. Only chloroform, which occurs after two reaction steps from tetrachloromethane, is relevant as a waste product for the assessment of the atomic economy. It should furthermore be kept in mind that the product of the reaction has a greater molar mass than the starting compound. The atom economy of this reaction can therefore be classified as relatively good.
The Atherton-Todd reaction is related to the Appel reaction. In the Appel reaction, tetrachloromethane is used for chlorination as well. [2]
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In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of an unobserved tautomer phosphorous acid, H3PO3, with the simplest example being trimethylphosphite, P(OCH3)3. Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH)2). The simplest representative is dimethylphosphite with the formula HP(O)(OCH3)2. Both classes of phosphites are usually colorless liquids.
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Diethyl chlorophosphate is an organophosphorus compound with the formula (C2H5O)2P(O)Cl. As an reagent in organic synthesis, it is use the convert alcohols to the corresponding diethylphosphate esters. It is a colorless liquid with a fruity odor. It is a corrosive, and as a cholinesterase inhibitor, highly toxic through dermal absorption. The molecule is tetrahedral.
Secondary is a term used in organic chemistry to classify various types of compounds or reactive intermediates. An atom is considered secondary if it has two 'R' Groups attached to it. An 'R' group is a carbon containing group such as a methyl. A secondary compound is most often classified on an alpha carbon or a nitrogen. The word secondary comes from the root word 'second' which means two.
Diethylphosphite is the organophosphorus compound with the formula (C2H5O)2P(O)H. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethylphosphite is a colorless liquid. The molecule is tetrahedral.
Dimethylphosphite is an organophosphorus compound with the formula (CH3O)2P(O)H, known as dimethyl hydrogen phosphite (DMHP). Dimethylphosphite, is a minor tautomer of the phosphorus(V) derivative. It is a reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. The molecule is tetrahedral. It is a colorless liquid. The compounds can be prepared by methanolysis of phosphorus trichloride or by heating diethylphosphite in methanol.
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