5 Key excerpts on "Carboxylic Acids"

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  eBook - ePub

  Enological Chemistry

  • Juan Moreno, Rafael Peinado(Authors)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Traditionally, acids in wine have been classified into two large groups according to their origin: those derived from the metabolism of the vine (of plant origin) and those derived from the metabolism of the microorganisms that control alcoholic fermentation. All common biological acids are organic compounds. The carboxyl group, which is characteristic of this family of compounds, is formed by a carbonyl group (C=O) and a hydroxyl group (−OH). These groups are located at one end of a carbon chain:

  The carboxyl group gives rise to the family of Carboxylic Acids and is usually represented in the forms shown above, where R1 may be a hydrogen atom, an alkyl radical, or an aryl radical (aromatic).

  The carbon atom of the carboxyl group uses three hybrid sp2 orbitals. These orbitals are all in the same plane, and the remaining p orbital of the carbon atom forms a Π bond with a p orbital of the oxygen in the carbonyl group, such that the group lies in a single plane and the hydrogen of the hydroxyl group lies outside that plane. It is important to understand the structure of the carboxyl functional group, since this forms the basis for a reasoned understanding of the most important property of these substances, namely acidity.

  Nomenclature

  According to IUPAC naming conventions, linear-chain acids are named by changing the “-e” suffix in the corresponding hydrocarbon to the suffix “-oic” and adding the word

  TABLE 8.1. Types of Carboxylic Acid

  R1	Acid	Formula
  H	Formic or methanoic acid (1st in the series)	H-COOH
  R-(alkyl radical)	Aliphatic carboxylic	R-COOH
  Ar-(aryl radical)	Aromatic carboxyl	Ar-COOH

  FIGURE 8.1 4-Ethyl heptanoic acid (not 4-propyl hexanoic acid).

  FIGURE 8.2 1,2,4-Butanyl tricarboxylic acid.

  acid

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  eBook - ePub

  Biochemistry

  An Organic Chemistry Approach

  • Michael B. Smith(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  , 55 , 6295–6303. Copyright 2016 American Chemical Society.

  3.7 Carboxylic Acid Derivatives and Acyl Substitution

  An important functional group has a carbon atom (alkyl group) attached to a carbonyl (C=O) functional group, but a hydroxyl (OH) group is also attached to the carbonyl carbon. This unit is known as a carboxyl group , which is the major structural feature of the class of organic molecules known as Carboxylic Acids . The interesting feature of the carboxyl functional group is the presence of the highly polarized O—H unit with the hydrogen δ+ shown in Figure 3.19 (the same as Figure 1.14). The polarization induced by the carboxyl oxygen makes the carboxyl carbon atom very positive, which leads to the oxygen of the OH unit being negatively polarized, and the hydrogen positively polarized as shown. In other words, the proton is acidic. The greater acidity of the carboxylic acid is largely due to the stability of the conjugate base that is formed.

  FIGURE 3.19 Ethanoic acid.

  There are four important derivatives of Carboxylic Acids in which the OH unit in RCOOH is replaced by a halogen, —O2 CR, —OR, or —NR2 , all attached to a carbonyl unit. The first type is an acid halide , generated when the OH unit in RCOOH is replaced with a halogen atom (e.g., chlorine, an acid chloride ). An acid anhydride is formed when the OH group is replaced by another acid unit (O2 CR). As the name suggests (anhydride = without water), anhydrides are essentially two carboxylic acid units joined together with loss of a water molecule. If the OH group in RCOOH is replaced by an OR′ group (from an alcohol), it is called an ester or a carboxylic ester. An ester is essentially a combination of a carboxylic acid and an alcohol. Finally, if OH in RCOOH is replaced with an amine group (NH2 , NHR1 , or NR1 R2 ), the derivative is called an amide . An amide is essentially a combination of a carboxylic acid and an amine. For each of these carboxylic acid derivatives, the unit that has replaced the OH unit is shown in violet. The structure of several acid derivatives and their names are shown in Table 3.1

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  eBook - ePub

  BIOS Instant Notes in Organic Chemistry

  • Graham Patrick(Author)
  • 2004(Publication Date)
  • Taylor & Francis

    (Publisher)

  This distinguishes Carboxylic Acids and their derivatives from aldehydes and ketones where the corresponding atom is hydrogen or carbon. This is important with respect to the sort of reactions which Carboxylic Acids and their derivatives undergo. The carboxylic acid group (COOH) is often referred to as a carboxyl group. Figure 1. (a) Acid chloride; (b) acid anhydride; (c) ester; (d) amide; (e) carboxylic acid. Figure 2. Structure of the functional group. Bonding The bonds in the carbonyl C=O group are made up of a strong σ bond and a weaker π bond (Figure 3). Since oxygen is more electronegative than carbon, the carbonyl group is polarized such that the oxygen is slightly negative and the carbon is slightly positive. This means that oxygen can act as a nucleophilic center and carbon can act as an electrophilic center. Figure 3. Bonding and properties. Properties Carboxylic Acids and their derivatives are polar molecules due to the polar carbonyl group and the presence of a heteroatom in the group Y. Carboxylic Acids can associate with each other as dimers (Figure 4) through the formation of two intermolecular hydrogen bonds which means that Carboxylic Acids have higher boiling points than alcohols of comparable molecular weight. It also means that low molecular weight Carboxylic Acids are soluble in water. However, as the molecular weight of the carboxylic acid increases, Figure 4. Intermolecular H-bonding. the hydrophobic character of the alkyl portion eventually outweighs the polar character of the functional group such that higher molecular weight Carboxylic Acids are insoluble in water. Primary amides and secondary amides also have a hydrogen capable of hydrogen bonding (i.e. , RCON H 2, RCON H R′), resulting in higher boiling points for these compounds compared to aldehydes and ketones of similar molecular weight. Acid chlorides, acid anhydrides, esters, and tertiary amides are polar, but lack a hydrogen atom capable of participating in hydrogen bonding

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  BIOS Instant Notes in Chemistry for Biologists

  • J Fisher, J.R.P. Arnold, Julie Fisher, John Arnold(Authors)
  • 2020(Publication Date)
  • Taylor & Francis

    (Publisher)

  4 ). The phosphoanhydride link is an important component of the nucleic acids. Di- and tries ter equivalents are found in the key energy sources for biological processes. Their anhydride equivalents, adenosine triphosphate (ATP) and adenosine diphosphate (ADP), are equally important.

  Related topics

  (F1) Phosphoric acid and phosphates (I2) Classification of organic reactions (I1) Reactive species

  Physical properties of acids

  The simplest Carboxylic Acids are generally liquids at room temperature with characteristic, and generally unpleasant, odors (Table 1 ). However, they are high boiling point liquids. As with alcohols (Sections I1 and J1) Carboxylic Acids are able to intermolecularly

  Table 1 Examples of naturally occurring Carboxylic Acids

  hydrogen bond. Carboxylic Acids generally have higher boiling points than alcohols of the same molecular weight, as hydrogen bonded acids are held together by two bonds; This ability to hydrogen bond makes the smaller Carboxylic Acids water soluble.

  Carboxylic acid dissociation

  Perhaps the most important property of Carboxylic Acids is their acidic behavior (Section N). In water, a proton leaves the acid, converting it to a carboxylate anion (Figure 1a ). Carboxylic Acids are relatively weak acids and therefore are only fractionally dissociated under normal aqueous conditions. However, when strong bases, such as sodium hydroxide or potassium hydroxide are present, Carboxylic Acids readily dissociate to form salts (Figure 1b ). These salts are generally solid at room temperature and water soluble. A number of carboxylic acid salts are used commercially as food preservatives. For example, calcium and sodium proprionate (CH3 CH2 COO− Na+ ) are used in the preservation of breads and cakes. Sodium benzoate (C6 H5 COO− Na+

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  eBook - ePub

  Industrial Microbiology

  • David B. Wilson, Hermann Sahm, Klaus-Peter Stahmann, Mattheos Koffas, David B. Wilson, Hermann Sahm, Klaus-Peter Stahmann, Mattheos Koffas(Authors)
  • 2019(Publication Date)
  • Wiley-VCH

    (Publisher)

  5 Organic Acids

  Michael Sauer and Diethard Mattanovich

  BOKU University of Natural Resources and Life Sciences, Department of Biotechnology, Muthgasse 18, 1190 Vienna, Austria

  CHAPTER MENU

  1. 5.1 Introduction
  2. 5.2 Citric Acid
  3. 5.3 Lactic Acid
  4. 5.4 Gluconic Acid
  5. 5.5 Succinic Acid
  6. 5.6 Itaconic Acid
  7. 5.7 Downstream Options for Organic Acids
  8. 5.8 Perspectives

  5.1 Introduction

  Organic acids are central players within the metabolism of all living cells (see Figure 5.1 for an overview). They are also prominent products accumulated by many microorganisms. The importance of organic acids in the biological world is based on the one hand on the wide variety of chemical reactions directly involving the carboxyl group and on the other hand on the buffering or acidifying capacity of this group, exhibiting the potential to modify the cell's chemical surroundings.

  The same reasons that make many organic acids important molecules in the cell render them useful in many other contexts, such as food production or the chemical industry. Indeed, biogenic acids – many of them are of microbial origin – are longtime companions of humankind. First, large‐scale productions were food‐related fermentations, where the acids have never been obtained in pure form. Examples are fermented vegetables such as sauerkraut or kimchi, which rely on the production of lactic acid by lactic acid bacteria. Another example is vinegar production from sweet juices. First, the sugar is fermented by yeasts, and then the produced ethanol is oxidized by acetic acid bacteria to acetic acid, which gives the characteristic taste and provides the antimicrobial activity, which is sought after.

  Figure 5.1

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