Problem 57 - Basic Principles of Organic Chemistry

Question

Write equations for a practical laboratory synthesis of each of the following substances from the indicated starting materials (several steps may be required). Give reagents and conditions. a. 2 -chloroethyl bromoethanoate from ethanol and/or ethanoic acid b. 2 -methoxy-2-methylpropanamide from 2 -methylpropanoic acid c. 3,5,5-trimethyl-3-hexanol from 2,4,4-trimethyl-1-pentene (commercially available) d. 3,3-dimethylbutanal from 2,2-dimethylpropanoic acid e. \(2,3,3\) -trimethyl-2-butanol from 2,3-dimethyl-2-butene

Step-by-Step Solution

Answer

Each compound has been synthesized by specific multi-step reactions using reagents like PBr₃, SOCl₂, DIBAL-H, and BH₃.

Step 1: Synthesis of 2-chloroethyl bromoethanoate

Starting with ethanol, first convert it into ethyl bromide (chloro group introduction).1. Convert ethanol to ethyl bromide: Treat ethanol with phosphorus tribromoide (PBr₃), obtaining ethyl bromide - Reaction: \( C_2H_5OH + PBr_3 \rightarrow C_2H_5Br + H_3PO_3 \).2. Convert ethyl bromide to ethyl chloroacetate: React ethyl bromide with silver acetate and then with thionyl chloride (SOCl₂) to obtain 2-chloroethyl bromoethanoate. - Reaction: \( C_2H_5Br + AgCH_3COO \rightarrow C_2H_5OOCCH_3 + AgBr \) and \( C_2H_5OOCCH_3 + SOCl_2 \rightarrow C_2H_5OCCCl + SO_2 + HCl \).Reagents: Phosphorus tribromoide (PBr₃), Silver acetate (AgCH₃COO), Thionyl chloride (SOCl₂).

Step 2: Synthesis of 2-methoxy-2-methylpropanamide

1. Start with 2-methylpropanoic acid and convert it to the corresponding acid chloride using thionyl chloride (SOCl₂). - Reaction: \( (CH_3)_2CHCOOH + SOCl_2 \rightarrow (CH_3)_2CHCOCl + SO_2 + HCl \) 2. Perform esterification by reacting the acid chloride with methanol to form the ester which further undergoes amidation. - Reaction: \( (CH_3)_2CHCOCl + CH_3OH \rightarrow (CH_3)_2CHCOOCH_3 + HCl \)3. Convert the ester to the amide using ammonia. - Reaction: \( (CH_3)_2CHCOOCH_3 + NH_3 \rightarrow (CH_3)_2CHCONH_2 + CH_3OH \)Reagents: Thionyl chloride (SOCl₂), Methanol (CH₃OH), Ammonia (NH₃).

Step 3: Synthesis of 3,5,5-trimethyl-3-hexanol

1. Begin with 2,4,4-trimethyl-1-pentene and perform hydration using a catalytic acid to introduce an alcohol group. - Reaction: \( C_8H_{16} + H_2O \rightarrow C_6H_{14}OH \).Reagents: Acid catalyst, Water.

Step 4: Synthesis of 3,3-dimethylbutanal

1. Begin with 2,2-dimethylpropanoic acid and perform oxidation of the acid to form 3,3-dimethylbutanoic acid. 2. Reduce the carboxylic acid to an aldehyde using DIBAL-H in low temperatures. - Reaction: \( (CH_3)_3CCOOH \xrightarrow{DIBAL-H} (CH_3)_3CCHO \)Reagents: DIBAL-H (Diisobutylaluminium hydride).

Step 5: Synthesis of 2,3,3-trimethyl-2-butanol

1. Start with 2,3-dimethyl-2-butene and perform hydroboration-oxidation process to convert it into the alcohol. - Reaction: \( C_6H_{12} + BH_3 \rightarrow C_6H_{12}B \rightarrow C_6H_{12}OH \) (where Borane BH₃ is used for hydroboration followed by oxidation with hydrogen peroxide and sodium hydroxide.)Reagents: Borane (BH₃), Hydrogen peroxide (H₂O₂), Sodium hydroxide (NaOH).

Key Concepts

Functional Group Transformation

In organic chemistry, functional group transformation refers to the conversion of one functional group in a molecule to another. This is a critical step in the process of synthesizing complex molecules as it enables chemists to derive new compounds with desired properties. For example, converting ethanol to ethyl bromide involves replacing the hydroxyl group with a bromo group. This is achieved using phosphorus tribromoide (PBr₃), where the

• Hydroxyl group (-OH) is transformed to bromo group (-Br).
• The reaction equation is: \( C_2H_5OH + PBr_3 \rightarrow C_2H_5Br + H_3PO_3 \).

Understanding these transformations helps in designing pathways for synthesizing target molecules. Another example is the conversion of acid chlorides to esters and then to amides, showcasing the versatility in functional group transformations.

Reagents and Conditions

The selection of reagents and conditions plays a vital role in the success of chemical transformations. Each reaction step requires specific chemicals and conditions to proceed efficiently. Let's look at the example of synthesizing 2-methoxy-2-methylpropanamide:

• Thionyl chloride (SOCl₂) is used to convert acids to acid chlorides.
• Methanol is used to convert acid chlorides to esters through esterification.
• Ammonia is employed for the amidation of esters to form amides.

The conditions often involve controlling factors such as temperature and pH. In the case of reducing carboxylic acids to aldehydes, DIBAL-H requires low temperatures to selectively achieve the desired reduction, minimizing over-reduction to alcohols. Correct reagents and conditions are crucial for effective chemical synthesis.

Multi-step Synthesis

Multi-step synthesis refers to the sequence of reactions required to convert starting materials into the final desired compound. Each intermediate can require different reagents and conditions, often building on the results of the preceding step. In the synthesis of 3,5,5-trimethyl-3-hexanol from 2,4,4-trimethyl-1-pentene, multi-step synthesis is employed: - The initial step involves hydration, where the alkene reacts with water under acidic conditions to form an alcohol. - Multi-step synthesis often demands careful planning as the order and efficiency of each step impacts the overall yield and purity of the final product. Breaking down the synthetic process into individual reactions makes it manageable and allows precise control over each stage.

Chemical Equations

Chemical equations are the language of chemistry, succinctly conveying information about the reactants, products, and conditions of a reaction. They help in visualizing and planning synthesis pathways. For example, the equation for hydroboration-oxidation converting 2,3-dimethyl-2-butene to an alcohol:- Initial hydroboration: \( C_6H_{12} + BH_3 \rightarrow C_6H_{12}B \)- Followed by oxidation: \( C_6H_{12}B \rightarrow C_6H_{12}OH \)- These equations indicate borane (BH₃) as a key reagent, followed by oxidation with hydrogen peroxide and sodium hydroxide.Equations describe the stoichiometry, which is pivotal for predicting the amounts of reactants needed and the products formed, facilitating the optimization of organic syntheses.