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

Gli oli vegetali e i grassi animali sono lipidi presenti in natura nelle piante o negli animali. Gli oli e i grassi sono spesso sotto forma di trigliceridi, che sono formati da una molecola di glicerolo e tre acidi grassi. Un acido grasso è un acido carbossilico debole con una catena idrocarburica come gruppo funzionale. Nel trigliceride, i tre acidi grassi sono legati alla molecola del glicerolo da legami estere. Un trigliceride, quindi, ha tre gruppi estere, rendendo la molecola un triestere.
Un estere è un tipo di molecola organica che è simile a un acido carbossilico, con l'idrogeno dell'ossidrile sostituito da un gruppo alchilico o arilico. Questo gruppo è etichettato come R-primo per mostrare che potrebbe essere diverso dal gruppo R sull'altro lato. In un trigliceride, R-prime è la spina dorsale del glicerolo e ogni gruppo R è la catena di un acido grasso.
Gli acidi grassi con doppi legami nelle loro catene di carbonio sono noti come acidi grassi insaturi. Questi doppi legami tendono ad essere nella conformazione cis, che mette una curva nella catena. I trigliceridi con queste catene piegate non possono combaciare strettamente, quindi le forze attrattive tra di loro sono tipicamente a lungo raggio e deboli.
Gli acidi grassi con solo legami singoli tra gli atomi di carbonio sono saturi. Queste catene non piegate consentono ai trigliceridi di impacchettarsi strettamente insieme, consentendo interazioni intermolecolari più forti e a corto raggio. Ciò conferisce ai trigliceridi saturi un punto di fusione più elevato rispetto ai trigliceridi insaturi, che di solito sono liquidi a temperatura ambiente.
I trigliceridi possono essere riconvertiti in acidi grassi e glicerolo idrolizzando i tre esteri. L'idrolisi dell'estere è una reazione che rompe un legame estere con una molecola d'acqua o uno ione idrossido per formare un acido carbossilico e un alcol. Un uso comune dell'idrolisi degli esteri è quello di creare saponi, che sono i sali degli acidi grassi dei trigliceridi. Questo processo è chiamato saponificazione.
In questa reazione, gli ioni idrossido attaccano ciascuno dei tre carbonili esteri nel trigliceride, producendo tre molecole di acido grasso e una molecola di glicerolo. I carbossilati degli acidi grassi si associano al controione della base, che di solito è sodio o potassio.
Ma come funziona il sapone? La lunga catena di carbonio è lipofila e idrofoba, il che significa che è attratta dai grassi ma non dall'acqua. Il gruppo carbossilato è idrofilo, il che significa che è attratto dall'acqua. Quando si mescolano acqua e sapone, le lunghe catene di carbonio tendono a interagire tra loro ed evitare l'interazione con le molecole d'acqua, mentre i gruppi carbossilati preferiscono interagire con l'acqua. Alla fine, le molecole di sapone formano gruppi chiamati micelle, con i carbossilati idrofili rivolti verso l'esterno.
Ora, supponiamo che ci sia grasso idrofobico sulle tue mani. Il semplice sciacquamento delle mani con acqua non rimuoverebbe il grasso. Quando ti lavi con il sapone, il grasso interagisce con le catene di carbonio del sapone. Quando le molecole di sapone formano le micelle, portano il grasso nel nucleo idrofobo racchiudendolo in un guscio idrofilo che può poi essere risciacquato con acqua.
In questo laboratorio, eseguirai una reazione di saponificazione per creare sapone dall'olio di cocco e dall'idrossido di sodio. Verificherai quindi la tolleranza del tuo sapone per l'acqua dura confrontando la capacità schiumogena nell'acqua deionizzata, nell'acqua del rubinetto e in una soluzione di cloruro di calcio, che imita l'acqua estremamente dura.

idrolisi di un estere

<h4>trigliceridi</h4>
I trigliceridi sono molecole triestere composte da una spina dorsale di glicerolo che è legata a 3 acidi grassi. Questi costituiscono la base di molti lipidi biologici che si trovano negli oli e nei grassi vegetali. I lipidi isolati dal materiale vegetale sono la base degli oli vegetali, mentre i lipidi estratti dagli animali sono usati come strutto o fonti generali di grassi.
Una molecola di acido grasso ha una lunga catena di atomi di carbonio - tra 12 e 20 atomi di carbonio - con un acido organico debole a un'estremità. Alcuni acidi grassi hanno doppi legami nella catena del carbonio. Si tratta di grassi "insaturi". A causa del doppio legame nella catena carboniosa, questi acidi grassi hanno tipicamente una forma a catena piegata, poiché il legame tende ad adottare la conformazione cis piuttosto che la conformazione trans.
Le molecole di trigliceridi in un acido grasso insaturo non sono in grado di impilarsi uniformemente, portando a una minore attrattiva delle forze tra le molecole. Pertanto, i grassi insaturi sono solitamente liquidi a temperatura ambiente. Al contrario, i grassi saturi, ovvero quelli con solo legami singoli nella loro catena di carbonio, sono in grado di accumularsi perché la loro catena ha una forma più regolare. I grassi saturi, quindi, hanno forze attrattive più forti tra le molecole e, di conseguenza, punti di fusione più elevati. Pertanto, i grassi saturi tendono ad essere solidi a temperatura ambiente.
<h4>Reazione di idrolisi</h4>
I trigliceridi, come altre molecole che possiedono gruppi esteri, sono in grado di subire idrolisi. L'idrolisi è un tipo di reazione chimica in cui una molecola d'acqua rompe un legame. Nel caso di un'idrolisi estere, il nucleofilo - acqua o uno ione idrossido - attacca il carbonio carbonilico del gruppo estere per rompere il legame estere. Un frammento della molecola originale ottiene lo ione idrogeno dall'acqua per formare un alcol, mentre l'altro frammento guadagna il gruppo idrossido per formare un sale dell'acido carbossilico.
In condizioni normali, si verificano solo poche reazioni di idrolisi senza l'aggiunta di un acido o di una base forte. L'acido o la base forte funge da catalizzatore per accelerare la reazione e viene recuperato alla fine. La reazione di idrolisi è reversibile. Si chiama reazione di condensazione perché produce acqua come prodotto collaterale.
L'idrolisi di un trigliceride è uno dei più antichi esempi di reazione di idrolisi, poiché è stato utilizzato per secoli per fare il sapone. La reazione è chiamata saponificazione.
<h4>saponificazione </h4>
Durante la saponificazione, gli ioni idrossido attaccano i gruppi carbonilici nei tre esteri del trigliceride. Pertanto, l'aggiunta stechiometrica di tre moli di idrossido di sodio a una mole di trigliceride provocherà l'idrolisi dei tre gruppi estere. Questa reazione produce tre moli di molecole di sapone e una mole di glicerolo. Spesso, la reazione verrà eseguita con idrossido di sodio come reagente limitante per ridurre al minimo la quantità di trigliceridi non reagiti, che può ridurre l'effetto essiccante del sapone.
Una molecola di sapone ha una lunga catena di carbonio idrofobica con un anione carbossilato idrofilo polare all'altra estremità. La differenza di solubilità lungo la molecola ne consente la capacità di pulizia. In acqua, le lunghe catene di carbonio delle molecole di sapone saranno attratte l'una dall'altra e si riorganizzeranno per evitare le molecole d'acqua polari. Questo orienta le teste polari del carbossilato verso le molecole d'acqua, formando una struttura sferica nota come micella. Il centro è idrofobo e l'esterno è idrofilo, consentendo alle micelle di essere solubili in soluzioni acquose.
Le proprietà micellari del sapone sono essenziali per la sua capacità di pulizia. Il semplice risciacquo del grasso o dell'olio da una superficie non può rimuoverlo. Questo perché il grasso è idrofobo e non solubile in acqua. Tuttavia, quando si usa il sapone, il grasso entra all'interno della micella. L'esterno della micella è idrofilo, quindi può essere risciacquato con acqua.
Uno svantaggio significativo del sapone è la sua intolleranza all'acqua dura. L'acqua dura è una soluzione acquosa contenente ioni magnesio, ferro e calcio sotto forma di minerali. La "durezza" dell'acqua dipende dalla concentrazione di questi ioni. In presenza di cationi metallici, le molecole di sapone interagiranno con le molecole e le faranno cadere dalla soluzione, formando un precipitato di sale più comunemente noto come schiuma di sapone.
<h4>referenze</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2012). Chimica e reattività chimica. Belmont, CA: Brooks/Cole, Cengage Learning.</li>
	<li style="font-size:17px">Silberg, M.S. (2015). Chimica: la natura molecolare della materia e il cambiamento. Boston, MA: McGraw Hill.</li>
	<li style="font-size:17px">Streiwiester, A., Heathcock, C.H., Kosower, E.M. (1998). Introduzione alla Chimica Organica. Upper Saddle River, NJ: Prentice Hall.</li>
</ol>

Idrolisi di un estere

Trigliceridi
I trigliceridi sono molecole triestere composte da una spina dorsale di glicerolo che è legata a 3 acidi grassi. Questi costituiscono la base di molti ...

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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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Video completi e incentrati sul curriculum sia per gli istruttori che per gli studenti nei corsi di laboratorio di Chimica introduttiva.

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Explore how triglycerides break down during saponification to form soap and glycerol, and learn how soap cleans grease and reacts in hard water.

Soap Formation from Triglycerides | JoVE K12

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Soap Formation from Triglycerides

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