Grignard synthesis of alcohol

Introduction

            The Grignard reaction is the only simple technique possible capable of producing main, secondary, and tertiary alcohols. To produce primary a alcohol, the Grignard reagent is reacted with formaldehyde, aldehyde to produce secondary alcohol and eventually, tertiary alcohol is produced by reacting with a ketone to a Grignard reagent. In this experiment, a Grignard reaction was performed, which is the addition of an organomagnesium halide (Grignard reagent) to a ketone or aldehyde to form a primary, secondary, or tertiary, or alcohol.

Grignard reagents are also used in the following important reactions: adding an excess of a Grignard reagent to an ester or lactone creates a tertiary alcohol in which two groups of alkyls are the same, and adding a Grignard reagent to a nitrile produces an intermediate metalloimine unsymmetric ketone.

Mechanism of the Grignard Reaction

Sterically obstructed substrates can react according to the SET mechanism, but the reaction is generally expected to proceed via a nucleophilic addition mechanism

Aldehydes and ketones Grignard reaction

The only simple process available that is capable of producing primary, secondary, and tertiary alcohols is the reaction of Grignard. To obtain a primary alcohol with two more carbon atoms than the first Grignard reaction, the Grignard reagent reacts with formaldehyde, which is an ethylene oxide. The kind of alcohol formed at the end of the reaction is decided by the carbonyl compound one began with. On the carbon atom, a main alcohol has only one alky group attached to the-OH group on it. It is an alcohol where the hydroxyl group is bound to a single R group of primary carbon atoms.

A secondary alcohol will be the next alcohol that is created. There are two alkyl groups in a secondary alcohol, which may be the same or different depending on the alkyl group composition, bound to the carbon atom with the OH group on it. By altering the composition of the Grignard reagents, the nature of a secondary alcohol could be affected, resulting in a transition of the CH3CH2 group into another alkyl group. The nature of the aldehyde that converts the CH3 group into another alkyl group may also be modified. A reaction of a Grignard reagent with some other aldehyde was conducted for a secondary alcohol, and the reaction proceeded as shown below.

Tertiary alcohol is the next alcohol that is produced. It has three alkyl groups with the -OH added attached to the carbon, which may be a blend of the same or distinct alkyl group. The tertiary alcohol nature may have various differences based on what is used. By altering the composition of the Grignard reagent that would shift the CH3CH2 compound to any other alkyl group, it can be altered.

A modification in the composition of the ketone that would change the CH3 groups into other alkyl groups that would be selected from the initial ketone could also modify it. Ketones consist of two alkyl groups bound to the double bond of carbon-oxygen where propanone is the easiest for tertiary alcohol, a Grignard reagent reaction with a ketone was conducted, and as seen below, the reaction occurred. The tertiary alcohol is formed by substitution of the R groups in the alcohol general formula made.

The experiment went well for the most part, but there were also complications that ended up impacting the findings. For starters, the reaction went a little too quickly when adding some of the reagents due to more drops coming in than expected, and while this had no impact on the finished product, during the experiment it made things a little less stable. Often the flask was not corked during the attachment, which produced a drop in yield, one factor that may have changed the final yield quantity. If the containers were not fully dry at the beginning of the trial, as Grignard reagents are highly water-sensitive, another factor that may have influenced this was.

The final thing was that when checking for the boiling point, it never actually reached 61⁰C, but there was such a decrease in liquid in the flask that the heating had to be stopped. This was confirmed because when performing day two of the reaction there was much less than 0.3 mL so had to perform the less accurate way of measuring the boiling point of the unknown.  The boiling point observed was 65⁰C – 70⁰C, however, since there were so many issues with this experiment the product could have had impurities in it that threw of the accuracy of the boiling point. This could have been fixed by taking more care in the first part so there would be more product for the second part.

References:

1. Grignard ReactionGrignard Reagents http://www.organic-           chemistry.org/namedreactions/grignard-reaction.shtm (accessed Apr 6, 2017).

2. Ruychev, V. Organic Chemistry Lab Manual CHEM 2071 , 2015th ed     

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