Xirius-CHEMISTRYOFBIFUNCTIONALCOMPOUNDS7-CHM211.pdf
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This document, titled "CHEMISTRY OF BIFUNCTIONAL COMPOUNDS" for the CHM211 course, provides a comprehensive introduction to organic compounds containing two different functional groups or two identical functional groups at different positions. It systematically explores various classes of bifunctional compounds, detailing their definitions, classifications, nomenclature, synthesis methods, and characteristic reactions. The document emphasizes how the presence and relative positions of two functional groups significantly influence the chemical and physical properties of these compounds, often leading to unique intramolecular reactions.
The content is structured to cover key categories such as hydroxy acids, keto acids, dicarboxylic acids, amino acids, and unsaturated acids. For each class, the document outlines common synthetic routes, including named reactions like the Reformatsky reaction, Strecker synthesis, Gabriel phthalimide synthesis, Perkin reaction, and Knoevenagel condensation. A significant focus is placed on the distinctive reactions that arise from the interaction between the two functional groups, particularly the effects of heating, which can lead to the formation of lactones, lactides, anhydrides, or cyclic ketones, depending on the functional groups and their relative positions.
Overall, the document serves as a foundational text for understanding the reactivity and synthetic utility of bifunctional compounds, which are crucial intermediates in organic synthesis and fundamental building blocks in biological systems. It highlights the principles governing their behavior, providing students with a solid understanding of how to predict and explain the chemical transformations of these complex molecules.
MAIN TOPICS AND CONCEPTS
- Definition: Bifunctional compounds are organic molecules that possess two different functional groups or two identical functional groups located at different positions within the same molecule.
- Importance: These compounds are vital in organic synthesis, serving as versatile intermediates. They are also fundamental building blocks in biological systems (e.g., amino acids, hydroxy acids in metabolism).
- Classification: The document classifies bifunctional compounds based on the nature of their functional groups, including:
* Hydroxy acids (containing -OH and -COOH groups)
* Keto acids (containing -C=O and -COOH groups)
* Dicarboxylic acids (containing two -COOH groups)
* Amino acids (containing -NH$_2$ and -COOH groups)
* Unsaturated acids (containing C=C and -COOH groups)
Hydroxy Acids- Definition: Organic compounds containing both a hydroxyl (-OH) group and a carboxyl (-COOH) group.
- Classification: Based on the relative position of the -OH group to the -COOH group:
* $\alpha$-hydroxy acids: -OH on the carbon adjacent to -COOH (e.g., Lactic acid).
* $\beta$-hydroxy acids: -OH on the second carbon from -COOH (e.g., 3-Hydroxypropanoic acid).
* $\gamma$-hydroxy acids: -OH on the third carbon from -COOH (e.g., 4-Hydroxybutanoic acid).
* $\delta$-hydroxy acids: -OH on the fourth carbon from -COOH (e.g., 5-Hydroxypentanoic acid).
- Nomenclature: Named as hydroxy derivatives of the parent carboxylic acid (e.g., 2-hydroxypropanoic acid for lactic acid).
- Synthesis:
* From Halo Acids: Hydrolysis of $\alpha$-halo acids with aqueous alkali.
$R-CH(X)-COOH + NaOH \rightarrow R-CH(OH)-COOH + NaX$
* From Cyanohydrins: Hydrolysis of cyanohydrins formed from aldehydes/ketones.
$R-CHO + HCN \rightarrow R-CH(OH)-CN \xrightarrow{H_2O/H^+} R-CH(OH)-COOH$
* From $\alpha$-Keto Acids: Reduction of $\alpha$-keto acids.
$R-CO-COOH \xrightarrow{H_2/Pt \text{ or } NaBH_4} R-CH(OH)-COOH$
* From $\alpha$-Amino Acids: Reaction with nitrous acid ($HNO_2$).
$R-CH(NH_2)-COOH + HNO_2 \rightarrow R-CH(OH)-COOH + N_2 + H_2O$
* Reformatsky Reaction: Reaction of an $\alpha$-halo ester with an aldehyde or ketone in the presence of zinc, followed by hydrolysis.
$R_1-CHO + Br-CH_2-COOR_2 \xrightarrow{Zn} R_1-CH(OZnBr)-CH_2-COOR_2 \xrightarrow{H_3O^+} R_1-CH(OH)-CH_2-COOH$
- Reactions:
* Reactions of -OH group: Esterification, oxidation (to keto acids), dehydration.
* Reactions of -COOH group: Salt formation, esterification, reduction.
* Effect of Heat:
* $\alpha$-hydroxy acids: Undergo intermolecular dehydration to form cyclic diesters called lactides.
$2 R-CH(OH)-COOH \xrightarrow{\Delta} \text{Lactide} + 2 H_2O$
* $\beta$-hydroxy acids: Undergo intramolecular dehydration to form $\alpha,\beta$-unsaturated acids.
$R-CH(OH)-CH_2-COOH \xrightarrow{\Delta} R-CH=CH-COOH + H_2O$
* $\gamma$- and $\delta$-hydroxy acids: Undergo intramolecular esterification to form cyclic esters called lactones (5- or 6-membered rings, respectively).
$HO-(CH_2)_n-COOH \xrightarrow{\Delta} \text{Lactone} + H_2O \quad (n=3 \text{ for } \gamma, n=4 \text{ for } \delta)$
Keto Acids- Definition: Organic compounds containing both a carbonyl (-C=O) group and a carboxyl (-COOH) group.
- Classification: Based on the relative position of the -C=O group to the -COOH group:
* $\alpha$-keto acids: -C=O on the carbon adjacent to -COOH (e.g., Pyruvic acid).
* $\beta$-keto acids: -C=O on the second carbon from -COOH (e.g., Acetoacetic acid).
* $\gamma$-keto acids: -C=O on the third carbon from -COOH (e.g., Levulinic acid).
- Nomenclature: Named as oxo derivatives of the parent carboxylic acid (e.g., 2-oxopropanoic acid for pyruvic acid).
- Synthesis:
* From $\alpha$-Hydroxy Acids: Oxidation of $\alpha$-hydroxy acids.
$R-CH(OH)-COOH \xrightarrow{Oxidation} R-CO-COOH$
* From $\alpha$-Amino Acids: Oxidative deamination.
$R-CH(NH_2)-COOH \xrightarrow{Oxidation} R-CO-COOH + NH_3$
* From $\alpha$-Halo Acids: Reaction with KCN, followed by hydrolysis and oxidation.
$R-CH(X)-COOH \xrightarrow{KCN} R-CH(CN)-COOH \xrightarrow{H_2O/H^+} R-CH(COOH)_2 \xrightarrow{Oxidation} R-CO-COOH$ (This is a simplified representation, often involves intermediate steps or different routes).
* From Esters (Claisen Condensation): $\beta$-keto esters are formed via Claisen condensation, which can then be hydrolyzed and decarboxylated to give $\beta$-keto acids.
$2 CH_3COOEt \xrightarrow{NaOEt} CH_3COCH_2COOEt \xrightarrow{H_3O^+} CH_3COCH_2COOH$
- Reactions:
* Reactions of -C=O group: Reduction (to hydroxy acids), reaction with HCN (cyanohydrin formation), reaction with hydroxylamine ($NH_2OH$) (oxime formation), reaction with phenylhydrazine ($C_6H_5NHNH_2$) (phenylhydrazone formation).
* Reactions of -COOH group: Salt formation, esterification, reduction.
* Effect of Heat:
* $\alpha$-keto acids: Undergo decarboxylation, often catalyzed by enzymes (e.g., pyruvic acid to acetaldehyde).
$R-CO-COOH \xrightarrow{\Delta} R-CHO + CO_2$
* $\beta$-keto acids: Easily undergo decarboxylation on heating, forming a ketone and carbon dioxide. This is due to the stability of the enol intermediate.
$R-CO-CH_2-COOH \xrightarrow{\Delta} R-CO-CH_3 + CO_2$
* $\gamma$-keto acids: On heating, can undergo cyclization to form cyclic ketones. (e.g., Levulinic acid can be converted to 2-methylcyclopent-2-enone under specific conditions, though direct cyclization to a cyclic ketone is less common than other reactions for $\gamma$-keto acids).
Dicarboxylic Acids- Definition: Organic compounds containing two carboxyl (-COOH) groups.
- Examples: Oxalic acid (ethanedioic acid), Malonic acid (propanedioic acid), Succinic acid (butanedioic acid), Glutaric acid (pentanedioic acid), Adipic acid (hexanedioic acid), Maleic acid (cis-butenedioic acid), Fumaric acid (trans-butenedioic acid), Phthalic acid (benzene-1,2-dicarboxylic acid).
- Nomenclature: Named by adding "-dioic acid" to the parent alkane name (e.g., butanedioic acid).
- Synthesis:
* From Dinitriles: Hydrolysis of dinitriles.
$NC-(CH_2)_n-CN \xrightarrow{H_2O/H^+} HOOC-(CH_2)_n-COOH$
* From Dihaloalkanes: Reaction with KCN, followed by hydrolysis.
$X-(CH_2)_n-X \xrightarrow{KCN} NC-(CH_2)_n-CN \xrightarrow{H_2O/H^+} HOOC-(CH_2)_n-COOH$
* From Cyclic Ketones: Oxidation of cyclic ketones.
$\text{Cyclohexanone} \xrightarrow{HNO_3} HOOC-(CH_2)_4-COOH \text{ (Adipic acid)}$
* From Unsaturated Acids: Oxidation of unsaturated acids (e.g., maleic acid to tartaric acid, though this is a dihydroxy dicarboxylic acid).
* Malonic Ester Synthesis: A versatile method for synthesizing substituted malonic acids.
$CH_2(COOEt)_2 \xrightarrow{NaOEt} Na^+[CH(COOEt)_2]^- \xrightarrow{RX} R-CH(COOEt)_2 \xrightarrow{H_3O^+/\Delta} R-CH_2-COOH + CO_2$ (This leads to a monocarboxylic acid after decarboxylation, but the intermediate is a substituted malonic acid).
- Reactions:
* General reactions of -COOH group: Salt formation, esterification, reduction.
* Effect of Heat: This is a characteristic reaction, highly dependent on the distance between the two carboxyl groups.
* Oxalic acid (1,2-dioic): Decarboxylation to formic acid and carbon dioxide.
$HOOC-COOH \xrightarrow{\Delta} HCOOH + CO_2$
* Malonic acid (1,3-dioic): Decarboxylation to acetic acid and carbon dioxide.
$HOOC-CH_2-COOH \xrightarrow{\Delta} CH_3COOH + CO_2$
* Succinic acid (1,4-dioic): Dehydration to form a cyclic anhydride (succinic anhydride).
$HOOC-(CH_2)_2-COOH \xrightarrow{\Delta} \text{Succinic Anhydride} + H_2O$
* Glutaric acid (1,5-dioic): Dehydration to form a cyclic anhydride (glutaric anhydride).
$HOOC-(CH_2)_3-COOH \xrightarrow{\Delta} \text{Glutaric Anhydride} + H_2O$
* Adipic acid (1,6-dioic): Cyclization to form a cyclic ketone (cyclopentanone) with decarboxylation.
$HOOC-(CH_2)_4-COOH \xrightarrow{\Delta} \text{Cyclopentanone} + CO_2 + H_2O$
* Pimelic acid (1,7-dioic): Cyclization to form a cyclic ketone (cyclohexanone) with decarboxylation.
$HOOC-(CH_2)_5-COOH \xrightarrow{\Delta} \text{Cyclohexanone} + CO_2 + H_2O$
Amino Acids- Definition: Organic compounds containing both an amino (-NH$_2$) group and a carboxyl (-COOH) group. They are the building blocks of proteins.
- Classification: Based on the relative position of the -NH$_2$ group to the -COOH group:
* $\alpha$-amino acids: -NH$_2$ on the carbon adjacent to -COOH (most common in proteins).
* $\beta$-amino acids: -NH$_2$ on the second carbon from -COOH.
* $\gamma$-amino acids: -NH$_2$ on the third carbon from -COOH (e.g., GABA).
- Nomenclature: Common names are widely used (e.g., Glycine, Alanine). Systematic names are also possible (e.g., 2-aminopropanoic acid).
- Synthesis:
* From $\alpha$-Halo Acids (Ammonolysis): Reaction of $\alpha$-halo acids with ammonia.
$R-CH(X)-COOH + 2 NH_3 \rightarrow R-CH(NH_2)-COOH + NH_4X$
* Strecker Synthesis: Reaction of an aldehyde with ammonia and hydrogen cyanide, followed by hydrolysis of the resulting $\alpha$-aminonitrile.
$R-CHO + NH_3 + HCN \rightarrow R-CH(NH_2)-CN \xrightarrow{H_2O/H^+} R-CH(NH_2)-COOH$
* Gabriel Phthalimide Synthesis: A method to synthesize primary amines, adaptable for $\alpha$-amino acids by reacting potassium phthalimide with an $\alpha$-halo ester, followed by hydrolysis and decarboxylation.
$\text{Phthalimide} \xrightarrow{KOH} \text{Potassium Phthalimide} \xrightarrow{R-CH(X)-COOR'} \text{N-alkylphthalimide} \xrightarrow{H_3O^+/\Delta} R-CH(NH_2)-COOH$
* Reductive Amination of $\alpha$-Keto Acids: Reaction of an $\alpha$-keto acid with ammonia in the presence of a reducing agent.
$R-CO-COOH + NH_3 \xrightarrow{H_2/Ni \text{ or } NaBH_3CN} R-CH(NH_2)-COOH$
- Reactions:
* Amphoteric Nature (Zwitterions): Amino acids exist as zwitterions (dipolar ions) in neutral solution, where the carboxyl group is deprotonated ($COO^-$) and the amino group is protonated ($NH_3^+$).
$R-CH(NH_2)-COOH \rightleftharpoons R-CH(NH_3^+)-COO^-$
* Reactions of -NH$_2$ group: Acylation (formation of amides), reaction with nitrous acid ($HNO_2$) (deamination, forming hydroxy acids), alkylation.
* Reactions of -COOH group: Esterification, salt formation, decarboxylation (to amines).
* Peptide Bond Formation: Condensation reaction between the carboxyl group of one amino acid and the amino group of another, forming an amide linkage (peptide bond).
$R_1-CH(NH_2)-COOH + R_2-CH(NH_2)-COOH \rightarrow R_1-CH(NH_2)-CO-NH-CH(R_2)-COOH + H_2O$
Unsaturated Acids- Definition: Organic compounds containing both a carbon-carbon double bond (C=C) and a carboxyl (-COOH) group.
- Examples: Acrylic acid (propenoic acid), Crotonic acid (but-2-enoic acid), Maleic acid (cis-butenedioic acid), Fumaric acid (trans-butenedioic acid).
- Classification: Based on the position of the double bond relative to the carboxyl group (e.g., $\alpha,\beta$-unsaturated acids, $\beta,\gamma$-unsaturated acids).
- Nomenclature: Named by replacing "-ane" with "-ene" in the parent alkane and adding "-oic acid" (e.g., propenoic acid).
- Synthesis:
* From $\beta$-Hydroxy Acids: Dehydration of $\beta$-hydroxy acids.
$R-CH(OH)-CH_2-COOH \xrightarrow{H_2SO_4/\Delta} R-CH=CH-COOH + H_2O$
* Perkin Reaction: Condensation of an aromatic aldehyde with an acid anhydride in the presence of a weak base to form $\alpha,\beta$-unsaturated aromatic acids.
$Ar-CHO + (R-CH_2-CO)_2O \xrightarrow{R-CH_2-COONa} Ar-CH=C(R)-COOH + R-CH_2-COOH$
* Knoevenagel Condensation: Condensation of an aldehyde or ketone with a compound containing an active methylene group (like malonic ester), followed by hydrolysis and decarboxylation.
$R-CHO + CH_2(COOEt)_2 \xrightarrow{\text{Base}} R-CH=C(COOEt)_2 \xrightarrow{H_3O^+/\Delta} R-CH=CH-COOH + CO_2 + 2 EtOH$
* Wittig Reaction: Reaction of an aldehyde or ketone with a phosphorus ylide to form an alkene. Can be adapted for unsaturated acids.
$R-CHO + Ph_3P=CH-COOH \rightarrow R-CH=CH-COOH + Ph_3P=O$
- Reactions:
* Reactions of C=C bond: Addition reactions (hydrogenation with $H_2/Ni$, addition of $HX$, $H_2O$, $X_2$). The carboxyl group can influence regioselectivity.
* Reactions of -COOH group: Salt formation, esterification, reduction.
* Michael Addition: $\alpha,\beta$-unsaturated carbonyl compounds (including acids) are susceptible to nucleophilic addition at the $\beta$-carbon.
* Diels-Alder Reaction: $\alpha,\beta$-unsaturated acids can act as dienophiles in Diels-Alder reactions.
KEY DEFINITIONS AND TERMS
* Bifunctional Compound: An organic molecule possessing two different functional groups or two identical functional groups at distinct positions. Their chemistry is often characterized by the interplay between these two groups.
* Hydroxy Acid: A compound containing both a hydroxyl (-OH) group and a carboxyl (-COOH) group. Their reactivity is influenced by the relative positions of these groups, especially concerning intramolecular reactions upon heating.
* Keto Acid: A compound containing both a carbonyl (-C=O) group and a carboxyl (-COOH) group. These are important intermediates in metabolism and organic synthesis, known for their ease of decarboxylation, particularly for $\beta$-keto acids.
* Dicarboxylic Acid: An organic compound containing two carboxyl (-COOH) groups. The distance between the two carboxyl groups critically determines their behavior upon heating, leading to anhydrides or cyclic ketones.
* Amino Acid: An organic compound containing both an amino (-NH$_2$) group and a carboxyl (-COOH) group. They are the fundamental building blocks of proteins and exhibit amphoteric properties due to the presence of both acidic and basic groups, existing as zwitterions in neutral solutions.
* Unsaturated Acid: An organic compound containing both a carbon-carbon double bond (C=C) and a carboxyl (-COOH) group. The double bond can undergo addition reactions, and its conjugation with the carboxyl group can influence reactivity (e.g., in Michael additions).
* Lactide: A cyclic diester formed by the intermolecular dehydration of two molecules of an $\alpha$-hydroxy acid upon heating.
* Lactone: A cyclic ester formed by the intramolecular esterification of $\gamma$- or $\delta$-hydroxy acids upon heating. These are typically 5- or 6-membered rings, respectively.
* Decarboxylation: A chemical reaction that removes a carboxyl group (-COOH) and releases carbon dioxide ($CO_2$). This reaction is characteristic of $\alpha$-keto acids, $\beta$-keto acids, and certain dicarboxylic acids (e.g., malonic acid).
* Zwitterion: A neutral molecule with both positive and negative charges, typically arising from the protonation of a basic group and deprotonation of an acidic group within the same molecule (e.g., amino acids in neutral solution).
* Peptide Bond: An amide linkage (-CO-NH-) formed by the condensation reaction between the carboxyl group of one amino acid and the amino group of another, forming the backbone of proteins.
* Reformatsky Reaction: A synthetic reaction used to prepare $\beta$-hydroxy esters (which can be hydrolyzed to $\beta$-hydroxy acids) by reacting an $\alpha$-halo ester with an aldehyde or ketone in the presence of zinc.
* Strecker Synthesis: A method for synthesizing $\alpha$-amino acids by reacting an aldehyde with ammonia and hydrogen cyanide, followed by hydrolysis of the resulting $\alpha$-aminonitrile.
* Gabriel Phthalimide Synthesis: A method for synthesizing primary amines, which can be adapted to prepare $\alpha$-amino acids by reacting potassium phthalimide with an $\alpha$-halo ester, followed by hydrolysis.
* Perkin Reaction: A condensation reaction between an aromatic aldehyde and an acid anhydride in the presence of a weak base to form $\alpha,\beta$-unsaturated aromatic acids.
* Knoevenagel Condensation: A condensation reaction between an aldehyde or ketone and a compound containing an active methylene group (e.g., malonic ester) to form $\alpha,\beta$-unsaturated compounds.
IMPORTANT EXAMPLES AND APPLICATIONS
- Lactic Acid (2-hydroxypropanoic acid): An $\alpha$-hydroxy acid, important in muscle metabolism (causes muscle soreness). Its ability to form lactides upon heating is a key reaction.
$2 CH_3-CH(OH)-COOH \xrightarrow{\Delta} \text{Lactide} + 2 H_2O$
- Pyruvic Acid (2-oxopropanoic acid): An $\alpha$-keto acid, a central intermediate in metabolic pathways like glycolysis. It readily undergoes decarboxylation to acetaldehyde.
$CH_3-CO-COOH \xrightarrow{\Delta} CH_3-CHO + CO_2$
- Acetoacetic Acid (3-oxobutanoic acid): A $\beta$-keto acid, known for its extreme instability and ease of decarboxylation to acetone upon heating, a process relevant in ketosis.
$CH_3-CO-CH_2-COOH \xrightarrow{\Delta} CH_3-CO-CH_3 + CO_2$
- Succinic Acid (butanedioic acid): A dicarboxylic acid, a key intermediate in the citric acid cycle. Upon heating, it forms succinic anhydride, a cyclic anhydride.
$HOOC-(CH_2)_2-COOH \xrightarrow{\Delta} \text{Succinic Anhydride} + H_2O$
- Adipic Acid (hexanedioic acid): A dicarboxylic acid used in the production of nylon. When heated, it undergoes cyclization and decarboxylation to form cyclopentanone.
$HOOC-(CH_2)_4-COOH \xrightarrow{\Delta} \text{Cyclopentanone} + CO_2 + H_2O$
- Glycine (2-aminoethanoic acid): The simplest $\alpha$-amino acid, a fundamental building block of proteins. It exists as a zwitterion in neutral solution and can form peptide bonds.
$H_2N-CH_2-COOH \rightleftharpoons H_3N^+-CH_2-COO^-$
- Acrylic Acid (propenoic acid): An $\alpha,\beta$-unsaturated acid, widely used in the production of polymers (e.g., polyacrylates). Its double bond is susceptible to addition reactions.
$CH_2=CH-COOH$
DETAILED SUMMARY
The "CHEMISTRY OF BIFUNCTIONAL COMPOUNDS" document for CHM211 provides a thorough exploration of organic molecules containing two functional groups, highlighting how their presence and relative positions dictate their unique chemical properties and reactivity. The document begins by defining bifunctional compounds as molecules with two distinct functional groups or two identical groups at different locations, emphasizing their significance as synthetic intermediates and biological building blocks.
The core of the document is structured around five major classes of bifunctional compounds: hydroxy acids, keto acids, dicarboxylic acids, amino acids, and unsaturated acids. For each class, a consistent framework is followed, detailing their definition, classification based on functional group proximity (e.g., $\alpha, \beta, \gamma$), systematic and common nomenclature, key synthetic routes, and characteristic reactions.
Hydroxy acids, containing both -OH and -COOH groups, are synthesized via methods like the hydrolysis of halo acids or cyanohydrins, reduction of $\alpha$-keto acids, or the Reformatsky reaction. Their reactions are particularly sensitive to the relative positions of the -OH and -COOH groups, especially upon heating. $\alpha$-hydroxy acids undergo intermolecular dehydration to form cyclic diesters called lactides, while $\beta$-hydroxy acids dehydrate intramolecularly to yield $\alpha,\beta$-unsaturated acids. $\gamma$- and $\delta$-hydroxy acids, due to favorable ring sizes, undergo intramolecular esterification to form 5- or 6-membered cyclic esters known as lactones.Keto acids, possessing both -C=O and -COOH groups, are synthesized through oxidation of $\alpha$-hydroxy acids, oxidative deamination of $\alpha$-amino acids, or via methods involving $\beta$-keto esters from Claisen condensation. Their reactivity includes typical carbonyl reactions (reduction, oxime formation) and carboxyl reactions. A defining feature is their susceptibility to decarboxylation upon heating: $\alpha$-keto acids decarboxylate to aldehydes, and $\beta$-keto acids readily decarboxylate to ketones and carbon dioxide, a process facilitated by the stability of the enol intermediate. $\gamma$-keto acids are noted to undergo cyclization to form cyclic ketones under heat, though this is a less common pathway compared to lactone formation for hydroxy acids.