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

Los ésteres son una clase de moléculas orgánicas que pueden tener un aroma afrutado o floral. La estructura de un éster es un carbonilo con un grupo alquilo o arilo en un lado y un oxígeno unido a otro grupo alquilo o arilo en el otro lado.
Dependiendo de los grupos alquilo o arilo, el éster puede adquirir muchas características diferentes. Por ejemplo, la reacción del glicerol y tres ácidos grasos, que son ácidos carboxílicos con largas cadenas de alquilo, da como resultado un triglicérido, que tiene tres grupos éster. Las largas cadenas de alquilo de los ácidos grasos dan a los triglicéridos un peso molecular muy alto. Por el contrario, los ésteres simples tienen un peso molecular bajo y grupos funcionales pequeños.
Los olores y sabores de las frutas y flores se atribuyen a ésteres simples. Incluso pequeños cambios en la estructura de un éster simple afectan en gran medida su fragancia. Por ejemplo, cambiar un grupo hidroxilo a una amina cambia el aroma de este éster de gaulteria a uva. Del mismo modo, el acetato de propilo huele a peras, mientras que el acetato de butilo, que solo tiene un carbono más en su cadena, huele a manzanas.
Una forma común de hacer un éster es la esterificación de Fischer, donde un ácido carboxílico y un alcohol reaccionan en presencia de un catalizador ácido para formar el éster y el agua. El grupo R y el carbonilo provienen del ácido carboxílico, y el grupo alcoxi o ariloxi con el R' proviene del alcohol. Esta reacción de esterificación es reversible. Con una mezcla 1 a 1 del ácido carboxílico y el alcohol, tiende a alcanzar el equilibrio con un rendimiento de aproximadamente el 70% del éster en el mejor de los casos.
Sin embargo, el principio de Le Chatelier nos permite aumentar el rendimiento del éster más allá de eso. El principio de Le Chatelier establece que cualquier sistema en equilibrio químico que esté sujeto a un cambio en la concentración, la presión, la temperatura o el volumen se ajustará a un nuevo equilibrio que contrarreste el cambio.
Por lo tanto, si aumentamos la concentración de uno de los reactivos en una reacción reversible, el equilibrio se desplazará en la dirección que disminuya su concentración. Esto da como resultado un mayor rendimiento del producto éster en equilibrio. Por lo tanto, podemos mejorar el rendimiento de la esterificación mediante el uso de una relación molar de 3:1 o 1:3 de ácido carboxílico a alcohol.
En este experimento, se realizará una esterificación de Fischer utilizando alcohol en exceso y ácido sulfúrico como catalizador. En esta reacción, la reactividad del ácido carboxílico se ve reforzada por el ácido sulfúrico, que protona el oxígeno del carbonilo. El alcohol es un nucleófilo que ataca el carbono del carbonilo para formar un intermediario. A continuación, el hidrógeno del alcohol se transfiere a un hidroxilo cercano. A continuación, el carbonilo se reforma, eliminando una molécula de agua. Finalmente, la desprotonación da como resultado un éster neutro.
En este laboratorio, realizará una reacción de esterificación de Fischer con un alcohol y ácido carboxílico desconocidos en una proporción molar de 3:1. A continuación, identificará el éster utilizando su olor, determinará el rendimiento e identificará los dos reactivos desconocidos en función de la estructura del éster.

esterificación

<h4>esteres</h4>
La estructura de un éster es un carbonilo con un grupo alquilo o arilo (R) en un lado, y un oxígeno unido a otro grupo alquilo o arilo (R') en el otro lado, representado por la fórmula general: RCOOR'. Los ésteres se pueden obtener comúnmente por una reacción de esterificación entre un ácido carboxílico y un alcohol. El grupo hidroxilo del ácido carboxílico es reemplazado por un grupo alquilo o arilo. Los ésteres simples, que tienen bajo peso molecular y pequeños grupos funcionales R y R', tienen olores y sabores a frutas y flores.
El ácido carboxílico más simple es el ácido fórmico (HCOOH), y el alcohol más simple es el metanol. Por lo tanto, el éster más simple formado a partir de la esterificación de estas dos moléculas es el formiato de metilo (HCOOCH3). El formiato de metilo se considera un derivado del ácido fórmico porque el grupo OH es reemplazado por el grupo OCH3. Las diferencias estructurales entre el formiato de metilo y el ácido fórmico dictan la diferencia en sus propiedades. Esto se debe a que las propiedades de la molécula dependen en gran medida de los grupos R y R'.
Los ésteres que se encuentran en frutas y flores se conocen como ésteres simples debido a la baja complejidad de su estructura en comparación con otros ésteres. Los grupos alquilo y arilo que se encuentran en estos ésteres influyen en gran medida en la fragancia que emiten; Por lo tanto, la adición de un carbono o un grupo funcional diferente puede afectar el aroma producido por el éster. Por ejemplo, el acetato de propilo (C5H10O2) tiene aroma a peras. Sin embargo, el acetato de butilo (C6H12O2), que solo tiene un carbono más en su cadena, huele a manzanas.
Los ésteres de cadena larga, es decir, aquellos con cadenas de alquilo largas, se llaman ácidos grasos. Los ácidos grasos son compuestos biológicos importantes que son esenciales para ciertos procesos biológicos. Los ácidos grasos también son una forma biológica de almacenamiento de energía. Cuando tres ácidos grasos reaccionan con el glicerol, forman un triglicérido, la forma más común de ácidos grasos. Los triglicéridos tienen un peso molecular muy alto y pueden estar muy ramificados. Su función y propiedades dependen de la longitud y los tipos de cadenas de alquilo incorporadas a su estructura. Uno de los usos industriales más comunes de los triglicéridos es en la producción de jabones y detergentes.
<h4>Reacción de esterificación</h4>
Los ésteres se forman a partir de una reacción de esterificación, y los ésteres simples se forman a través de la esterificación de Fisher. Esta reacción convierte un ácido carboxílico y el alcohol en un éster con agua como subproducto. La esterificación de Fisher es una reacción reversible que procede muy lentamente. Se agrega un catalizador ácido, generalmente en forma de ácido sulfúrico, para aumentar la velocidad de la reacción y al mismo tiempo actúa como agente deshidratante.
El mecanismo de acción de una esterificación de Fisher comienza cuando el oxígeno carbonílico ataca al ácido sulfúrico y desprotona su grupo OH. Esto conduce a un oxígeno carbonílico cargado positivamente. Para estabilizar mejor la carga positiva, un par de electrones del doble enlace de carbonilo es empujado al oxígeno carbonilo mientras que simultáneamente crea un centro de carbono pobre en electrones. A continuación, el grupo hidroxilo del alcohol actúa como nucleófilo y ataca al carbono pobre en electrones, el electrófilo, formando un intermediario. Luego, el grupo hidroxilo cargado positivamente del alcohol es desprotonado por el grupo hidroxilo del ácido carboxílico, estabilizando el átomo de oxígeno del alcohol. En el último paso, el oxígeno carbonilo es desprotonado por la base conjugada, y el par de electrones libres se mueve hacia el centro carbonilo mientras que el grupo carboxilo protonado se va como una molécula de agua.
Dado que la reacción de esterificación es reversible, una mezcla 1:1 del ácido carboxílico y el alcohol alcanzará el equilibrio con un rendimiento de aproximadamente el 70% del éster. Sin embargo, como con cualquier proceso de equilibrio, la reacción se puede conducir en una dirección cambiando la concentración, la presión, la temperatura o el volumen de los reactivos. Este cambio hace que la reacción se ajuste a un nuevo equilibrio para contrarrestar el cambio, que es la base del principio de Le Chatelier.
Cuando se aumenta la concentración de uno de los reactivos, el equilibrio cambia en la dirección que disminuirá su concentración. Por lo tanto, al aumentar la concentración de un reactivo, el equilibrio produce más producto, lo que resulta en un mayor rendimiento del producto éster.
Un método común utilizado en los laboratorios de química orgánica es proporcionar un exceso de uno de los reactivos, generalmente el alcohol. Como se mencionó anteriormente, la esterificación de Fisher puede utilizar ácido sulfúrico como catalizador. Sin embargo, una de las otras funciones del ácido sulfúrico es actuar como agente deshidratante, secuestrando las moléculas de agua lejos de la reacción. La aplicación del principio de Le Chatelier demuestra que a medida que se elimina uno de los productos, en este caso, el agua, la reacción se ve impulsada a producir más producto. Esto aumenta el rendimiento del éster formado.
<h4>referencia</h4>
<ol>
	<li style="font-size:17px">Streitwieser, A., Heathcock, C.H., Kosower, E.M. (1998). Introducción a la Química Orgánica. Upper Saddle River, Nueva Jersey: Prentice Hall.</li>
</ol>

Esterificación

Esteres
La estructura de un éster es un carbonilo con un grupo alquilo o arilo (R) en un lado, y un oxígeno unido a otro grupo alquilo o arilo (R') ...

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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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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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