Name: soap formation from triglycerides
Uploaded: 2020-03-26T07:22:28.000Z
Duration: 4 min 10 s
Channel: JoVE

Pflanzliche Öle und tierische Fette sind natürlich vorkommende Lipide in Pflanzen oder Tieren. Öle und Fette liegen häufig in Form von Triglyceriden vor, die aus einem Molekül aus Glycerin und drei Fettsäuren gebildet werden. Eine Fettsäure ist eine schwache Carbonsäure mit einer Kohlenwasserstoffkette als funktionelle Gruppe. Im Triglycerid sind die drei Fettsäuren durch Esterbindungen mit dem Molekül Glycerin verbunden. Ein Triglycerid hat also drei Estergruppen, was das Molekül zu einem Triester macht.
Ein Ester ist eine Art organisches Molekül, das wie eine Carbonsäure ist, wobei der Wasserstoff des Hydroxyls durch eine Alkyl- oder Arylgruppe ersetzt wird. Diese Gruppe wird als R-Primzahl bezeichnet, um zu zeigen, dass sie sich von der R-Gruppe auf der anderen Seite unterscheiden kann. In einem Triglycerid ist R-Prime das Glycerin-Rückgrat, und jede R-Gruppe ist die Kette einer Fettsäure.
Fettsäuren mit Doppelbindungen in ihren Kohlenstoffketten werden als ungesättigte Fettsäuren bezeichnet. Diese Doppelbindungen befinden sich in der Regel in der cis-Konformation, die eine Biegung in die Kette bringt. Triglyceride mit diesen gebogenen Ketten können nicht eng zusammenpassen, so dass die Anziehungskräfte zwischen ihnen typischerweise weitreichend und schwach sind.
Fettsäuren, die nur Einfachbindungen zwischen den Kohlenstoffatomen haben, sind gesättigt. Diese ungebogenen Ketten ermöglichen es, dass sich die Triglyceride eng aneinander drängen, was stärkere, kurzreichweitige intermolekulare Wechselwirkungen ermöglicht. Dadurch haben gesättigte Triglyceride einen höheren Schmelzpunkt als ungesättigte Triglyceride, die bei Raumtemperatur in der Regel flüssig sind.
Triglyceride können durch Hydrolyse der drei Ester wieder in Fettsäuren und Glycerin umgewandelt werden. Die Esterhydrolyse ist eine Reaktion, bei der eine Esterbindung mit einem Wassermolekül oder einem Hydroxidion aufgebrochen wird, um eine Carbonsäure und einen Alkohol zu bilden. Eine häufige Anwendung der Esterhydrolyse ist die Herstellung von Seifen, bei denen es sich um die Salze von Fettsäuren aus Triglyceriden handelt. Dieser Vorgang wird als Verseifung bezeichnet.
Bei dieser Reaktion greifen Hydroxid-Ionen jedes der drei Estercarbonyle im Triglycerid an, wobei drei Fettsäuremoleküle und ein Molekül Glycerin entstehen. Die Fettsäurecarboxylate assoziieren mit dem Gegenion von der Base, bei der es sich normalerweise um Natrium oder Kalium handelt.
Doch wie funktioniert Seife? Die lange Kohlenstoffkette ist lipophil und hydrophob, was bedeutet, dass sie von Fetten, aber nicht von Wasser angezogen wird. Die Carboxylatgruppe ist hydrophil, was bedeutet, dass sie von Wasser angezogen wird. Wenn Sie Seife und Wasser mischen, neigen die langen Kohlenstoffketten dazu, miteinander zu interagieren und Wechselwirkungen mit Wassermolekülen zu vermeiden, während die Carboxylatgruppen bevorzugt mit Wasser interagieren. Letztendlich bilden die Seifenmoleküle Cluster, die Mizellen genannt werden, wobei die hydrophilen Carboxylate nach außen zeigen.
Nehmen wir nun an, dass sich hydrophobes Fett an Ihren Händen befindet. Wenn Sie Ihre Hände einfach mit Wasser abspülen, wird das Fett nicht entfernt. Beim Waschen mit Seife interagiert das Fett mit den Kohlenstoffketten der Seife. Wenn die Seifenmoleküle Mizellen bilden, bringen sie das Fett in den hydrophoben Kern und umschließen es mit einer hydrophilen Hülle, die dann mit Wasser abgespült werden kann.
In diesem Labor führen Sie eine Verseifungsreaktion durch, um Seife aus Kokosöl und Natriumhydroxid herzustellen. Anschließend testen Sie die Verträglichkeit Ihrer Seife gegenüber hartem Wasser, indem Sie die Schaumfähigkeit in entionisiertem Wasser, Leitungswasser und einer Kalziumchloridlösung vergleichen, die extrem hartes Wasser nachahmt.

hydrolyse eines esters

<h4>triglyceride</h4>
Triglyceride sind Triestermoleküle, die aus einem Glycerin-Rückgrat bestehen, das an 3 Fettsäuren gebunden ist. Diese bilden die Grundlage für viele biologische Lipide, die in pflanzlichen Ölen und Fetten enthalten sind. Lipide, die aus pflanzlichem Material isoliert werden, sind die Basis von Pflanzenölen, während Lipide, die aus Tieren gewonnen werden, als Schmalz oder allgemeine Fettquellen verwendet werden.
Ein Fettsäuremolekül hat eine lange Kohlenstoffkette – zwischen 12 und 20 Kohlenstoffatomen – mit einer schwachen organischen Säure an einem Ende. Einige Fettsäuren haben Doppelbindungen in der Kohlenstoffkette. Dabei handelt es sich um "ungesättigte" Fette. Aufgrund der Doppelbindung in der Kohlenstoffkette haben diese Fettsäuren typischerweise eine gebogene Kettenform, da die Bindung eher die cis-Konformation als die trans-Konformation annimmt.
Die Triglyceridmoleküle in einer ungesättigten Fettsäure können nicht gleichmäßig stapeln, was zu weniger anziehenden Kräften zwischen den Molekülen führt. So sind ungesättigte Fette bei Raumtemperatur in der Regel flüssig. Im Gegensatz dazu können gesättigte Fette, d. h. solche mit nur einfachen Bindungen in ihrer Kohlenstoffkette, gestapelt werden, da ihre Kette regelmäßiger geformt ist. Gesättigte Fette haben daher stärkere Anziehungskräfte zwischen den Molekülen und damit höhere Schmelzpunkte. Daher neigen gesättigte Fette dazu, bei Raumtemperatur fest zu sein.
<h4>Hydrolyse-Reaktion</h4>
Triglyceride sind wie andere Moleküle, die Estergruppen besitzen, in der Lage, sich einer Hydrolyse zu unterziehen. Hydrolyse ist eine Art chemischer Reaktion, bei der ein Wassermolekül eine Bindung aufbricht. Bei einer Esterhydrolyse greift das Nukleophil – Wasser oder ein Hydroxidion – den Carbonylkohlenstoff der Estergruppe an, um die Esterbindung aufzubrechen. Ein Fragment des ursprünglichen Moleküls gewinnt das Wasserstoffion aus dem Wasser, um einen Alkohol zu bilden, während das andere Fragment die Hydroxidgruppe gewinnt, um ein Salz der Carbonsäure zu bilden.
Unter normalen Bedingungen finden nur wenige Hydrolysereaktionen ohne Zugabe einer starken Säure oder Base statt. Die starke Säure oder Base wirkt als Katalysator, um die Reaktion zu beschleunigen, und wird am Ende zurückgewonnen. Die Hydrolysereaktion ist reversibel. Sie wird als Kondensationsreaktion bezeichnet, da als Nebenprodukt Wasser entsteht.
Die Hydrolyse eines Triglycerids ist eines der ältesten Beispiele für eine Hydrolysereaktion, da sie seit Jahrhunderten zur Herstellung von Seife verwendet wird. Die Reaktion wird als Verseifung bezeichnet.
<h4>Verseifung </h4>
Bei der Verseifung greifen Hydroxid-Ionen die Carbonylgruppen in den drei Estern des Triglycerids an. Daher führt die stöchiometrische Zugabe von drei Mol Natriumhydroxid zu einem Mol Triglycerid zur Hydrolyse der drei Estergruppen. Bei dieser Reaktion entstehen drei Mol Seifenmoleküle und ein Mol Glycerin. Häufig wird die Reaktion mit Natriumhydroxid als begrenzendem Reagenz durchgeführt, um die Menge an nicht umgesetzten Triglyceriden zu minimieren, was die Trocknungswirkung von Seife verringern kann.
Ein Seifenmolekül hat eine lange hydrophobe Kohlenstoffkette mit einem polaren hydrophilen Carboxylat-Anion am anderen Ende. Der Unterschied in der Löslichkeit entlang des Moleküls ermöglicht seine Reinigungsfähigkeit. Im Wasser werden die langen Kohlenstoffketten der Seifenmoleküle aneinander angezogen und organisieren sich neu, um die polaren Wassermoleküle zu vermeiden. Dadurch richten sich die polaren Carboxylatköpfe in Richtung der Wassermoleküle aus und bilden eine kugelförmige Struktur, die als Mizelle bekannt ist. Das Zentrum ist hydrophob und das Äußere hydrophil, so dass Mizellen in wässrigen Lösungen löslich sind.
Die Mizelleneigenschaften der Seife sind entscheidend für ihre Reinigungsfähigkeit. Das einfache Abspülen von Fett oder Öl von einer Oberfläche kann es nicht entfernen. Das liegt daran, dass Fett hydrophob und nicht wasserlöslich ist. Bei der Verwendung von Seife gelangt das Fett jedoch in das Innere der Mizelle. Das Äußere der Mizelle ist hydrophil, so dass sie mit Wasser abgespült werden kann.
Ein wesentlicher Nachteil der Seife ist ihre Unverträglichkeit gegenüber hartem Wasser. Hartes Wasser ist eine wässrige Lösung, die Magnesium-, Eisen- und Kalziumionen in Form von Mineralien enthält. Die "Härte" von Wasser hängt von der Konzentration dieser Ionen ab. In Gegenwart von metallischen Kationen interagieren Seifenmoleküle mit den Molekülen und führen dazu, dass sie aus der Lösung fallen, wodurch ein Salzniederschlag entsteht, der allgemein als Seifenschaum bezeichnet wird.
<h4>Referenzen</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr., P.M., Townsend, J.R. (2012). Chemie und chemische Reaktivität. Belmont, Kalifornien: Brooks/Cole, Cengage Lernen.</li>
	<li style="font-size:17px">Silberg, M.S. (2015). Chemie: Die molekulare Natur von Materie und Veränderung. Boston, MA: McGraw Hill.</li>
	<li style="font-size:17px">Streiwiester, A., Heathcock, C.H., Kosower, E.M. (1998). Einführung in die Organische Chemie. Upper Saddle River, NJ: Prentice Hall.</li>
</ol>

Hydrolyse eines Esters

Triglyceride
Triglyceride sind Triestermoleküle, die aus einem Glycerin-Rückgrat bestehen, das an 3 Fettsäuren gebunden ist. Diese bilden die Grundlage für viele biologische ...

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Hydrolysis of an Ester

soap formation from triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats.

A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result, unsaturated triglycerides do not stack evenly and have weaker attractions between molecules. They are usually liquid at room temperature. Saturated fats have only single bonds. Their chains are more regular, so they stack more easily. This gives them stronger attractions and higher melting points, which is why they are often solid at room temperature.

Triglycerides can also undergo hydrolysis because they contain ester groups. Hydrolysis is a reaction in which water breaks a bond. In ester hydrolysis, a nucleophile such as water or a hydroxide ion attacks the carbonyl carbon of the ester. One part of the molecule becomes an alcohol after gaining a hydrogen ion from water. The other part becomes a salt of a carboxylic acid after gaining the hydroxide group. Under normal conditions, only a few hydrolysis reactions occur without a strong acid or base. The acid or base acts as a catalyst and is recovered at the end. This reaction is reversible. It is also called a condensation reaction because water is formed as a side product.

The hydrolysis of triglycerides is one of the oldest examples of this chemistry and has been used for centuries to make soap. This reaction is called saponification. During saponification, hydroxide ions attack the carbonyl groups in the three ester bonds of the triglyceride. With three moles of sodium hydroxide for one mole of triglyceride, all three ester groups can be hydrolyzed. The products are three moles of soap molecules and one mole of glycerol. In practice, sodium hydroxide is often the limiting reagent so less triglyceride is left over. That helps reduce the drying effect of the soap.

Soap Formation from Triglycerides

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Soap Formation from Triglycerides

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