Name: ester formation and everyday fragrances
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 48 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.8

SC.912.P.8.13

Esterification

Ester sind eine Klasse organischer Moleküle, die ein fruchtiges oder blumiges Aroma haben können. Die Struktur eines Esters ist ein Carbonyl mit einer Alkyl- oder Arylgruppe auf der einen Seite und einem Sauerstoff, der an eine andere Alkyl- oder Arylgruppe gebunden ist, auf der anderen Seite.
Je nach Alkyl- oder Arylgruppe kann der Ester viele verschiedene Eigenschaften annehmen. Zum Beispiel ergibt die Reaktion von Glycerin und drei Fettsäuren, bei denen es sich um Carbonsäuren mit langen Alkylketten handelt, ein Triglycerid, das drei Estergruppen aufweist. Die langen Alkylketten aus den Fettsäuren verleihen den Triglyceriden ein sehr hohes Molekulargewicht. Im Gegensatz dazu haben einfache Ester ein niedriges Molekulargewicht und kleine funktionelle Gruppen.
Die Gerüche und Aromen von Früchten und Blüten werden auf einfache Ester zurückgeführt. Schon kleine Veränderungen in der Struktur eines einfachen Esters beeinflussen seinen Duft stark. Wenn beispielsweise eine Hydroxylgruppe in ein Amin umgewandelt wird, ändert sich der Duft dieses Esters von Wintergrün zu Traube. In ähnlicher Weise riecht Propylacetat nach Birnen, während Butylacetat, das nur einen weiteren Kohlenstoff in seiner Kette hat, nach Äpfeln riecht.
Eine gängige Methode zur Herstellung eines Esters ist die Fischer-Veresterung, bei der eine Carbonsäure und ein Alkohol in Gegenwart eines Säurekatalysators reagieren, um den Ester und das Wasser zu bilden. Die R-Gruppe und das Carbonyl stammen aus der Carbonsäure, und die Alkoxy- oder Aryloxygruppe mit dem R' stammt aus dem Alkohol. Diese Veresterungsreaktion ist reversibel. Mit einem 1 zu 1 Gemisch aus der Carbonsäure und dem Alkohol neigt es dazu, ein Gleichgewicht mit bestenfalls einer Ausbeute von etwa 70 % des Esters zu erreichen.
Das Prinzip von Le Chatelier ermöglicht es uns jedoch, die Ausbeute des Esters darüber hinaus zu erhöhen. Das Prinzip von Le Chatelier besagt, dass jedes System im chemischen Gleichgewicht, das einer Änderung der Konzentration, des Drucks, der Temperatur oder des Volumens ausgesetzt ist, sich an ein neues Gleichgewicht anpasst, das der Änderung entgegenwirkt.
Wenn wir also die Konzentration eines der Reaktanten in einer reversiblen Reaktion erhöhen, verschiebt sich das Gleichgewicht in die Richtung, die seine Konzentration verringert. Dies führt zu einer höheren Ausbeute des Esterprodukts im Gleichgewicht. Auf diese Weise können wir die Veresterungsausbeute verbessern, indem wir ein molares Verhältnis von Carbonsäure zu Alkohol von 3:1 oder 1:3 verwenden.
In diesem Experiment wird eine Fischer-Veresterung mit Alkoholüberschuss und Schwefelsäure als Katalysator durchgeführt. Bei dieser Reaktion wird die Carbonsäurereaktivität durch Schwefelsäure verstärkt, die den Sauerstoff des Carbonyls protoniert. Der Alkohol ist ein Nukleophil, das den Kohlenstoff des Carbonyls angreift und ein Zwischenprodukt bildet. Als nächstes wird der Wasserstoff des Alkohols auf ein nahegelegenes Hydroxyl übertragen. Das Carbonyl reformiert sich dann und eliminiert ein Wassermolekül. Schließlich entsteht durch die Deprotonierung ein neutraler Ester.
In diesem Labor führen Sie eine Fischer-Veresterungsreaktion mit einem unbekannten Alkohol und Carbonsäure in einem molaren Verhältnis von 3:1 durch. Anschließend identifizieren Sie den Ester anhand seines Geruchs, bestimmen die Ausbeute und identifizieren die beiden unbekannten Reagenzien anhand der Struktur des Esters.

veresterung

<h4>Ester</h4>
Die Struktur eines Esters ist ein Carbonyl mit einer Alkyl- oder Arylgruppe (R) auf der einen Seite und einem Sauerstoff, der an eine andere Alkyl- oder Arylgruppe (R') auf der anderen Seite gebunden ist, dargestellt durch die allgemeine Formel: RCOOR'. Ester können üblicherweise durch eine Veresterungsreaktion zwischen einer Carbonsäure und einem Alkohol abgeleitet werden. Die Hydroxylgruppe der Carbonsäure wird durch eine Alkyl- oder Arylgruppe ersetzt. Einfache Ester, die ein niedriges Molekulargewicht und kleine funktionelle R- und R'-Gruppen aufweisen, haben Gerüche und Aromen von Früchten und Blüten.
Die einfachste Carbonsäure ist Ameisensäure (HCOOH), wobei der einfachste Alkohol Methanol ist. Der einfachste Ester, der aus der Veresterung dieser beiden Moleküle gebildet wird, ist also das Methylformiat (HCOOCH3). Methylformiat wird als Derivat der Ameisensäure angesehen, da die OH-Gruppe durch die OCH3-Gruppe ersetzt wird. Die strukturellen Unterschiede zwischen Methylformiat und Ameisensäure bestimmen den Unterschied in ihren Eigenschaften. Denn die Eigenschaften des Moleküls hängen stark von den R- und R'-Gruppen ab.
Ester, die in Früchten und Blüten vorkommen, werden aufgrund der geringen Komplexität ihrer Struktur im Vergleich zu anderen Estern als einfache Ester bezeichnet. Die Alkyl- und Arylgruppen, die auf diesen Estern zu finden sind, beeinflussen den Duft, den sie abgeben, stark. Die Zugabe eines Kohlenstoffs oder einer anderen funktionellen Gruppe kann also den vom Ester erzeugten Duft beeinflussen. Propylacetat (C5H10O2) hat zum Beispiel den Duft von Birnen. Butylacetat (C6H12O2), das nur noch einen Kohlenstoff mehr in seiner Kette hat, riecht jedoch nach Äpfeln.
Langkettige Ester, also solche mit langen Alkylketten, werden als Fettsäuren bezeichnet. Fettsäuren sind wichtige biologische Verbindungen, die für bestimmte biologische Prozesse essentiell sind. Fettsäuren sind auch eine biologische Form der Energiespeicherung. Wenn drei Fettsäuren mit Glycerin reagieren, bilden sie ein Triglycerid – die häufigste Form von Fettsäuren. Triglyceride haben ein sehr hohes Molekulargewicht und können stark verzweigt sein. Ihre Funktion und Eigenschaften hängen von der Länge und Art der Alkylketten ab, die in ihre Struktur eingearbeitet sind. Eine der häufigsten industriellen Anwendungen von Triglyceriden ist die Herstellung von Seifen und Waschmitteln.
<h4>Veresterungsreaktion</h4>
Ester werden durch eine Veresterungsreaktion gebildet, wobei einfache Ester durch Fisher-Veresterung gebildet werden. Bei dieser Reaktion werden eine Carbonsäure und ein Alkohol in einen Ester umgewandelt, wobei Wasser als Nebenprodukt entsteht. Die Fisher-Veresterung ist eine reversible Reaktion, die sehr langsam abläuft. Ein saurer Katalysator, typischerweise in Form von Schwefelsäure, wird zugesetzt, um die Reaktionsgeschwindigkeit zu erhöhen und gleichzeitig als Entwässerungsmittel zu wirken.
Der Wirkmechanismus für eine Fisher-Veresterung beginnt damit, dass der Carbonylsauerstoff die Schwefelsäure angreift und ihre OH-Gruppe deprotoniert. Dies führt zu einem positiv geladenen Carbonylsauerstoff. Um die positive Ladung besser zu stabilisieren, wird ein Elektronenpaar der Carbonyl-Doppelbindung an den Carbonylsauerstoff gedrückt, während gleichzeitig ein elektronenarmes Kohlenstoffzentrum entsteht. Als nächstes wirkt die Hydroxygruppe des Alkohols als Nukleophil und greift den elektronenarmen Kohlenstoff – das Elektrophil – an, wodurch ein Zwischenprodukt gebildet wird. Dann wird die positiv geladene Hydroxylgruppe aus dem Alkohol durch die Hydroxylgruppe der Carbonsäure deprotoniert, wodurch das Sauerstoffatom des Alkohols stabilisiert wird. Im letzten Schritt wird der Carbonylsauerstoff durch die konjugierte Base deprotoniert, und das freie Elektronenpaar wird in Richtung des Carbonylzentrums bewegt, während die protonierte Carboxylgruppe als Wassermolekül austritt.
Da die Veresterungsreaktion reversibel ist, erreicht ein 1:1-Gemisch aus der Carbonsäure und dem Alkohol ein Gleichgewicht mit etwa 70 % Ausbeute des Esters. Wie bei jedem Gleichgewichtsprozess kann die Reaktion jedoch in eine Richtung gesteuert werden, indem die Konzentration, der Druck, die Temperatur oder das Volumen der Reagenzien geändert werden. Diese Veränderung bewirkt, dass sich die Reaktion an ein neues Gleichgewicht anpasst, um der Veränderung entgegenzuwirken, was die Grundlage des Prinzips von Le Chatelier ist.
Wenn die Konzentration eines der Reaktanten erhöht wird, verschiebt sich das Gleichgewicht in die Richtung, die seine Konzentration verringert. Durch die Erhöhung der Konzentration eines Reaktanten produziert das Gleichgewicht also mehr von dem Produkt, wodurch eine höhere Ausbeute des Esterprodukts zur Folge hat.
Eine gängige Methode, die in Labors der organischen Chemie verwendet wird, besteht darin, einen Überschuss an einem der Reagenzien, typischerweise dem Alkohol, bereitzustellen. Wie bereits erwähnt, kann bei der Fisher-Veresterung Schwefelsäure als Katalysator verwendet werden. Eine der anderen Funktionen von Schwefelsäure besteht jedoch darin, als Dehydratisierungsmittel zu wirken und Wassermoleküle von der Reaktion fernzuhalten. Die Anwendung des Prinzips von Le Chatelier zeigt, dass, wenn eines der Produkte – in diesem Fall Wasser – entfernt wird, die Reaktion zur Herstellung von mehr Produkt vorangetrieben wird. Dadurch erhöht sich die Ausbeute des gebildeten Esters.
<h4>Referenz</h4>
<ol>
	<li style="font-size:17px">Streitwieser, A., Heathcock, C.H., Kosower, E.M. (1998). Einführung in die Organische Chemie. Upper Saddle River, NJ: Prentice Hall.</li>
</ol>

Veresterung

Ester
Die Struktur eines Esters ist ein Carbonyl mit einer Alkyl- oder Arylgruppe (R) auf der einen Seite und einem Sauerstoff, der an eine andere Alkyl- oder Arylgruppe (R') gebunden ist ...

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ester formation and everyday fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group.

Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl formate, the simplest ester from these two molecules. Methyl formate is a derivative of formic acid because the OH group is replaced by OCH3. Small changes in the R and R' groups can also change the properties and scent of an ester.

This is why similar esters can smell different. Propyl acetate has a pear-like scent, while butyl acetate smells like apples, even though the molecules differ by only one carbon. Long-chain esters are called fatty acids. They are important in biology and also serve as a form of energy storage.

When three fatty acids react with glycerol, they form a triglyceride. Triglycerides are the most common form of fatty acids and have a high molecular weight. They can also be highly branched. Their function and properties depend on the length and type of alkyl chains in their structure. Triglycerides are widely used in industry, including the production of soaps and detergents.

Simple esters are often made by Fischer esterification, which is a slow and reversible reaction. It converts a carboxylic acid and an alcohol into an ester and water. Sulfuric acid is commonly used as an acid catalyst. It speeds up the reaction and also acts as a dehydrating agent.

The reaction mechanism starts when the carbonyl oxygen interacts with sulfuric acid and becomes positively charged. The carbonyl double bond then shifts electron density toward the oxygen, leaving the carbonyl carbon more electron-poor. Next, the alcohol acts as a nucleophile and attacks that carbon, forming an intermediate. The alcohol oxygen is then deprotonated, and the carbonyl oxygen is finally deprotonated as water leaves.

Because Fischer esterification is reversible, a 1:1 mixture of the acid and alcohol reaches equilibrium at about 70% ester yield. The reaction can be pushed toward more ester by changing concentration, pressure, temperature, or volume. This follows Le Chatelier's principle, which says a system shifts to counter a change. In the lab, using excess alcohol is a common way to increase yield. Sulfuric acid also helps by removing water, and taking away this product drives the reaction to make more ester.

Ester Formation and Everyday Fragrances

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A physical property is ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

Clausius-Clapeyron Equation

The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

SC.912.P.8.2

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

The Wave Nature of Light

The nature of light has been a subject of inquiry since antiquity. In the seventeenth century, Isaac Newton performed experiments with lenses and prisms ...

The Electromagnetic Spectrum

The electromagnetic spectrum consists of all the types of electromagnetic radiation arranged according to their frequency and wavelength. Each of the ...

Interference and Diffraction

Interference is a characteristic phenomenon exhibited by waves. When two electromagnetic waves interact with their peaks and troughs coinciding, a ...

Photoelectric Effect

When light of a particular wavelength strikes a metal surface, electrons are emitted. This is called the photoelectric effect. The minimum frequency of ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a ...

The Uncertainty Principle

Werner Heisenberg considered the limits of how accurately one can measure properties of an electron or other microscopic particles. He determined that ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Explore the scientific theory of atoms (also known as atomic theory) by describing changes in the atomic model over time and why those changes were necessitated by experimental evidence.

SC.912.P.8.3

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Atomic Number and Mass Number

The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element. Its value determines the identity of ...

Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom.

SC.912.P.8.4

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

Electron Configurations

Electron configurations and orbital diagrams can be determined by applying the Aufbau principle (each added electron occupies the subshell of lowest ...

Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central&#160;core called the nucleus, with electrons present around the ...

Relate properties of atoms and their position in the periodic table to the arrangement of their electrons.

SC.912.P.8.5

A. A working definition of matter is that it takes up space, has mass, and has measurable properties. Matter is comprised of atomic, subatomic, and elementary particles.

B. Electrons are key to defining chemical and some physical properties, reactivity, and molecular structures. Repeating (periodic) patterns of physical and chemical properties occur among elements that define groups of elements with similar properties. The periodic table displays the repeating patterns, which are related to the atom's outermost electrons. Atoms bond with each other to form compounds.

C. In a chemical reaction, one or more reactants are transformed into one or more new products. Many factors shape the nature of products and the rates of reaction. 

D. Carbon-based compounds are building-blocks of known life forms on earth and numerous useful natural and synthetic products.

Ester Formation and Everyday Fragrances

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