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

Estry to klasa cząsteczek organicznych, które mogą mieć owocowy lub kwiatowy aromat. Struktura estru to karbonyl z grupą alkilową lub arylową z jednej strony i tlenem związanym z inną grupą alkilową lub arylową z drugiej strony.
W zależności od grup alkilowych lub arylowych, ester może przybierać wiele różnych cech. Na przykład w wyniku reakcji glicerolu i trzech kwasów tłuszczowych, które są kwasami karboksylowymi o długich łańcuchach alkilowych, powstaje trójgliceryd, który ma trzy grupy estrowe. Długie łańcuchy alkilowe z kwasów tłuszczowych nadają trójglicerydom bardzo wysoką masę cząsteczkową. Natomiast proste estry mają niską masę cząsteczkową i małe grupy funkcyjne.
Zapachy i smaki owoców i kwiatów przypisuje się prostym estrom. Nawet niewielkie zmiany w strukturze prostego estru mają duży wpływ na jego zapach. Na przykład zmiana grupy hydroksylowej na aminę zmienia zapach tego estru z wintergreenowego na winogronowy. Podobnie octan propylu pachnie jak gruszki, podczas gdy octan butylu, który ma w swoim łańcuchu tylko jeszcze jeden węgiel, pachnie jak jabłka.
Jednym z powszechnych sposobów wytwarzania estru jest estryfikacja Fischera, w której kwas karboksylowy i alkohol reagują w obecności katalizatora kwasowego, tworząc ester i wodę. Grupa R i karbonyl pochodzą z kwasu karboksylowego, a grupa alkoksylowa lub aryloksylowa z R' pochodzi z alkoholu. Ta reakcja estryfikacji jest odwracalna. Przy mieszaninie 1 do 1 kwasu karboksylowego i alkoholu ma tendencję do osiągania równowagi z około 70% wydajnością estru w najlepszym przypadku.
Jednak zasada Le Chateliera pozwala nam zwiększyć wydajność estru ponad to. Zasada Le Chateliera mówi, że każdy układ w równowadze chemicznej, który jest poddany zmianie stężenia, ciśnienia, temperatury lub objętości, dostosuje się do nowej równowagi, która przeciwdziała zmianie.
Jeśli więc zwiększymy stężenie jednego z reagentów w reakcji odwracalnej, równowaga przesunie się w kierunku, który zmniejsza jego stężenie. Powoduje to wyższą wydajność produktu estrowego w stanie równowagi. W ten sposób możemy poprawić wydajność estryfikacji, stosując stosunek molowy kwasu karboksylowego do alkoholu wynoszący 3:1 lub 1:3.
W tym eksperymencie zostanie przeprowadzona estryfikacja Fischera przy użyciu nadmiaru alkoholu i kwasu siarkowego jako katalizatora. W tej reakcji reaktywność kwasu karboksylowego jest wzmacniana przez kwas siarkowy, który protonuje tlen karbonylu. Alkohol jest nukleofilem, który atakuje węgiel karbonylu, tworząc produkt pośredni. Następnie wodór z alkoholu jest przenoszony do pobliskiego hydroksylu. Karbonyl następnie przekształca się, eliminując cząsteczkę wody. Wreszcie, deprotonacja powoduje powstanie neutralnego estru.
W tym laboratorium przeprowadzisz reakcję estryfikacji Fischera z nieznanym alkoholem i kwasem karboksylowym w stosunku molowym 3:1. Następnie zidentyfikujesz ester na podstawie jego zapachu, określisz wydajność i zidentyfikujesz dwa nieznane odczynniki na podstawie struktury estru.

estryfikacji

<h4>estry</h4>
Struktura estru to karbonylek z grupą alkilową lub arylową (R) po jednej stronie i tlenem związanym z inną grupą alkilową lub arylową (R') po drugiej stronie, reprezentowaną przez ogólny wzór: RCOOR'. Estry można powszechnie uzyskać w reakcji estryfikacji między kwasem karboksylowym a alkoholem. Grupa hydroksylowa kwasu karboksylowego jest zastępowana grupą alkilową lub arylową. Proste estry, które mają niską masę cząsteczkową i małe grupy funkcyjne R i R', mają zapachy i smaki owoców i kwiatów.
Najprostszym kwasem karboksylowym jest kwas mrówkowy (HCOOH), a najprostszym alkoholem jest metanol. Tak więc najprostszym estrem powstałym w wyniku estryfikacji tych dwóch cząsteczek jest mrówczan metylu (HCOOCH3). Mrówczan metylu jest uważany za pochodną kwasu mrówkowego, ponieważ grupa OH jest zastąpiona grupą OCH3. Różnice strukturalne między mrówczanem metylu a kwasem mrówkowym dyktują różnicę w ich właściwościach. Dzieje się tak, ponieważ właściwości cząsteczki zależą w dużym stopniu od grup R i R'.
Estry, które znajdują się w owocach i kwiatach, są znane jako estry proste ze względu na niską złożoność ich struktury w porównaniu z innymi estrami. Grupy alkilowe i arylowe znajdujące się na tych estrach mają ogromny wpływ na wydzielany przez nie zapach; W związku z tym dodanie węgla lub innej grupy funkcyjnej może mieć wpływ na zapach wytwarzany przez ester. Na przykład octan propylu (C, 5, H, 10,O2) ma zapach gruszek. Jednak octan butylu (C, 6, H,12O2), który ma w swoim łańcuchu tylko jeden węgiel więcej, pachnie jabłkami.
Estry długołańcuchowe, czyli te o długich łańcuchach alkilowych, nazywane są kwasami tłuszczowymi. Kwasy tłuszczowe są ważnymi związkami biologicznymi, które są niezbędne dla niektórych procesów biologicznych. Kwasy tłuszczowe są również biologiczną formą magazynowania energii. Kiedy trzy kwasy tłuszczowe reagują z glicerolem, tworzą trójgliceryd - najczęstszą formę kwasów tłuszczowych. Trójglicerydy mają bardzo dużą masę cząsteczkową i mogą być silnie rozgałęzione. Ich funkcja i właściwości są zależne od długości i rodzaju łańcuchów alkilowych wbudowanych w ich strukturę. Jednym z najczęstszych przemysłowych zastosowań trójglicerydów jest produkcja mydeł i detergentów.
<h4>Reakcja estryfikacji</h4>
Estry powstają w wyniku reakcji estryfikacji, przy czym proste estry powstają w wyniku estryfikacji Fishera. Ta reakcja przekształca kwas karboksylowy i alkohol w ester z wodą jako produktem ubocznym. Estryfikacja Fishera jest reakcją odwracalną, która przebiega bardzo powoli. Katalizator kwasowy, zwykle w postaci kwasu siarkowego, jest dodawany w celu zwiększenia szybkości reakcji, działając jednocześnie jako środek odwadniający.
Mechanizm działania estryfikacji Fishera rozpoczyna się od ataku tlenu karbonylowego na kwas siarkowy i deprotonacji jego grupy OH. Prowadzi to do dodatnio naładowanego tlenu karbonylowego. Aby lepiej ustabilizować ładunek dodatni, jedna para elektronów podwójnego wiązania karbonylowego jest popychana do tlenu karbonylowego, jednocześnie tworząc ubogie w elektrony centrum węglowe. Następnie grupa hydroksylowa alkoholu działa jak nukleofil i atakuje węgiel ubogi w elektrony - elektrofil - tworząc produkt pośredni. Następnie dodatnio naładowana grupa hydroksylowa z alkoholu jest deprotonowana przez grupę hydroksylową kwasu karboksylowego, stabilizując atom tlenu alkoholu. W ostatnim etapie tlen karbonylowy jest deprotonowany przez sprzężoną zasadę, a para wolnych elektronów jest przesuwana w kierunku środka karbonylowego, podczas gdy protonowana grupa karboksylowa opuszcza się jako cząsteczka wody.
Ponieważ reakcja estryfikacji jest odwracalna, mieszanina kwasu karboksylowego i alkoholu w stosunku 1:1 osiągnie równowagę z około 70% wydajnością estru. Jednak, podobnie jak w przypadku każdego procesu równowagi, reakcja może być prowadzona w jednym kierunku poprzez zmianę stężenia, ciśnienia, temperatury lub objętości odczynników. Ta zmiana powoduje, że reakcja dostosowuje się do nowej równowagi, aby przeciwdziałać zmianie, która jest podstawą zasady Le Chateliera.
Gdy stężenie jednego z reagentów wzrasta, równowaga przesuwa się w kierunku, który zmniejszy jego stężenie. Tak więc, zwiększając stężenie jednego reagenta, równowaga wytwarza więcej produktu, co skutkuje wyższą wydajnością produktu estrowego.
Jedną z powszechnych metod stosowanych w laboratoriach chemii organicznej jest dostarczanie nadmiaru jednego z odczynników, zwykle alkoholu. Jak wspomniano wcześniej, estryfikacja Fishera może wykorzystywać kwas siarkowy jako katalizator. Jednak jedną z innych funkcji kwasu siarkowego jest działanie jako środek odwadniający, sekwestrujący cząsteczki wody z dala od reakcji. Zastosowanie zasady Le Chateliera pokazuje, że gdy jeden z produktów jest usuwany – w tym przypadku woda – reakcja jest popychana do wytworzenia większej ilości produktu. Zwiększa to wydajność powstałego estru.
<h4>odniesienie</h4>
<ol>
	<li style="font-size:17px">Streitwieser, A., Heathcock, C.H., Kosower, E.M. (1998). Wprowadzenie do chemii organicznej. Upper Saddle River, NJ: Prentice Hall.</li>
</ol>

Estryfikacji

Estry
Struktura estru to karbonylek z grupą alkilową lub arylową (R) po jednej stronie i tlenem związanym z inną grupą alkilową lub arylową (R') ...

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JoVE Lab Manual

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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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Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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Learn how carboxylic acids and alcohols form esters, why some smell fruity, and how Fischer esterification uses sulfuric acid to boost yield.

Ester Formation and Everyday Fragrances | JoVE K12

Przygotuj się do nauczania Estryfikacji dzięki temu 4-minutowemu przewodnikowi dla instruktorów. Obejmuje kluczowe kroki przygotowawcze dla laboratorium Chemistry na JoVE Lab Manual.

Przygotowanie instruktora do Estryfikacji w Chemistry - Ponad 10K wyświetleń | JoVE Lab Manual

Postępuj zgodnie z procedurami Estryfikacji krok po kroku w tym 10-minutowym filmie z protokołem studenckim. Część kolekcji Chemistry na JoVE Lab Manual.

Protokół studencki dla Estryfikacji w Chemistry - Ponad 20K wyświetleń | JoVE Lab Manual

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

States of Matter

Solids, liquids, and gases are the three states of matter commonly found on Earth. A solid is rigid and possesses a definite shape. A liquid flows and ...

States of Matter and Phase Changes

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

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Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Differentiate between physical and chemical properties and physical and chemical changes of matter.

SC.912.P.8.1

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Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

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. ...

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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.

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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.

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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 ...

Electron Behavior

Electrons are negatively charged subatomic particles that are attracted to an orbit around the positively-charged nucleus of an atom. They reside in ...

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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