Name: alcohol tests for primary, secondary, and tertiary
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 32 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.8

SC.912.P.8.13

Identifying Alcohols

Alkohole sind eine Klasse organischer Moleküle, die mindestens eine funktionelle Hydroxylgruppe besitzen, die mit einem Kohlenstoffatom verbunden ist. Methanol und Ethanol sind zwei bekannte Alkohole. Beide sind aliphatische Alkohole, was bedeutet, dass sie von einem Kohlenwasserstoff abgeleitet sind und keine Benzolgruppe enthalten.
Es gibt drei Klassifikationen von aliphatischen Alkoholen. Der erste ist ein primärer Alkohol, bei dem die Hydroxylgruppe mit einem Kohlenstoffatom verbunden ist, das wiederum mit einer kohlenstoffbasierten oder Alkylgruppe verbunden ist. In einem sekundären Alkohol ist die Hydroxylgruppe mit einem Kohlenstoffatom verbunden, das zwei Alkylgruppen hat. In einem tertiären Alkohol schließlich ist die Hydroxylgruppe mit einem Kohlenstoffatom mit drei Alkylgruppen verbunden.
Alkohole können auch aromatisch sein, wobei eine Hydroxylgruppe direkt mit dem Kohlenstoff eines Benzolrings verbunden ist. Die einfachste Form eines aromatischen Alkohols ist Phenol. Verbindungen, die Phenol enthalten, werden als Phenolderivate oder Phenole bezeichnet.
Bestimmte Reaktionen, die Alkohole hervorrufen, können verwendet werden, um sie anhand sichtbarer Unterschiede im Ergebnis der Reaktion zu unterscheiden. Eine solche Reaktion ist der Eisenchlorid-Test, der auf das Vorhandensein von Phenolen testet. Wenn Eisenchlorid zu einem Phenol hinzugefügt wird, bildet sich ein violetter Eisen-Drei-Phenol-Komplex. Dies wird nicht beobachtet, wenn es einem aliphatischen Alkohol zugesetzt wird.
Eine weitere nützliche Reaktion ist der Jones-Test, der zur Identifizierung von primären und sekundären aliphatischen Alkoholen verwendet wird. Das Jones-Reagenz, eine Mischung aus Schwefelsäure und Chromtrioxid in Wasser, ist ein starkes Oxidationsmittel. Es reagiert mit primären Alkoholen zu Aldehyden – die dann Carbonsäuren bilden – und es reagiert mit sekundären Alkoholen zu Ketonen. Die Zugabe des Jones-Reagenzes zu primären und sekundären Alkoholen bewirkt, dass die Lösung ihre Farbe von orange nach dunkelgrün ändert. Tertiäre Alkohole reagieren nicht mit dem Jones-Reagenz, da sie oxidationsbeständig sind.
Schließlich können wir mit dem Lucas-Test aliphatische Alkohole unterscheiden. Das Lucas-Reagenz, das ein Gemisch aus Zinkchlorid und Salzsäure ist, reagiert mit sekundären und tertiären Alkoholen durch eine nukleophile Substitutionsreaktion SN1. Das Zinkchlorid koordiniert sich mit dem Hydroxylsauerstoff, um eine ausgezeichnete Abgangsgruppe zu erzeugen. Nach der Eliminierung verbleibt ein positiv geladener Karbon. Dann greift ein Chlorion das Carbokation an und bildet ein Alkylchlorid, das in Wasser unlöslich ist und trüb erscheint.
Tertiäre Alkohole reagieren sofort mit dem Lucas-Reagenz und bilden bei Raumtemperatur eine ölige Schicht. Sekundäre Alkohole liefern nach einigen Sekunden bis einigen Minuten ein positives Ergebnis. Primäre Alkohole liefern ein negatives Ergebnis, wenn sie nicht erhitzt werden.
In diesem Labor verwenden Sie den Eisenchlorid-Test, den Jones-Test und den Lucas-Test, um einen unbekannten Alkohol zu identifizieren.

identifizierung von alkoholen

<h4>Alkohole</h4>
Alkohole sind organische Verbindungen, die zu den bekanntesten und bekanntesten gehören, da sie vielfältige Anwendungen und Verwendungen im Alltag haben. Alkohole sind organische Moleküle, die eine funktionelle Hydroxylgruppe enthalten, die mit einer Alkyl- oder Arylgruppe (ROH) verbunden ist. Hat der Hydroxylkohlenstoff nur eine einzige R-Gruppe, wird er als primärer Alkohol bezeichnet. Wenn er zwei R-Gruppen hat, ist er ein sekundärer Alkohol, und wenn er drei R-Gruppen hat, ist er ein tertiärer Alkohol. Wie viele andere organische Verbindungen können auch Alkohole aromatisch sein, indem sie einen Benzolring enthalten. Der einfachste aromatische Alkohol ist Phenol.
Die Identifizierung eines Alkohols in der organischen Chemie kann durch die Ausnutzung der unterschiedlichen Eigenschaften der Arten von Alkoholen erreicht werden. Während verschiedene instrumentelle Analysemethoden, wie z. B. die Kernspinresonanz (NMR), verwendet werden können, können auch andere qualitative Tests verwendet werden. Durch die Kopplung dieser Tests kann die Identität eines Alkohols auf ähnliche Weise bestimmt werden, wie Aldehyde und Ketone identifiziert werden können.
<h4>Eisenchlorid-Test</h4>
Eine Methode, um zwischen einem aliphatischen Alkohol und einem aromatischen Alkohol zu unterscheiden, ist die Verwendung von Eisen(III)-chlorid. Die Eisenchloridverbindung verleiht der Lösung ein rot-orangefarbenes Aussehen. In Gegenwart eines aromatischen Alkohols, wie z.B. Phenol, werden die Chloridatome durch den aromatischen Alkohol ersetzt, wodurch sich die Koordinationseigenschaft des zentralen Eisenatoms ändert. Dadurch ändert sich die Farbe der Lösung in eine violette Farbe. Aliphatische Alkohole reagieren nicht mit Eisen(III)-chlorid und daher bleibt die Lösung rot-orange.
<h4>Jones-Test</h4>
Im Rahmen des Jones-Tests wird Chromtrioxid in Gegenwart von Schwefelsäure verwendet, um als starkes Oxidationsmittel zu wirken. In Gegenwart des Jones-Reagenzes wird ein primärer Alkohol zuerst in einen Aldehyd und dann in eine Carbonsäure umgewandelt, während ein sekundärer Alkohol zu einem Keton oxidiert wird. Die Oxidationsstufe von Chrom ist der Schlüssel zu diesem Test. Chrom befindet sich im Jones-Reagenz in der Oxidationsstufe +6. Die Cr(VI)-Komplexe im Reagenz verleihen ihm seine leuchtend rötliche, orange Farbe.
Im Verlauf der Reaktion wird Chrom von Cr(VI) auf die Oxidationsstufe +3 — Cr(III) reduziert. Zunächst bilden der Alkohol und die Chromsäure einen Chromatester. Dann spaltet eine Base (H2O) die C-H-Bindung des Alkohols und bildet die Carbonylgruppe, während Cr(VI) zu Cr(IV) reduziert wird. Der Kohlenstoff des Alkohols erfährt eine 2-Elektronen-Oxidation und der Cr(IV) eine 2-Elektronen-Reduktion, so dass es sich um einen Reduktions-Oxidationsschritt handelt.
Cr(IV) beteiligt sich an weiteren Oxidationsschritten und wird schließlich zu Cr(III) reduziert. Cr(III) liegt häufig in Form von Hexaaquachrom(III)-Ionen — [Cr(H2O)6]3+ — und Cr(III)-Komplexen vor, wobeiH2O-Moleküle durch ein oder mehrere Sulfationen ersetzt werden — [Cr(H2O)5(SO4)]+. Diese Komplexe verleihen Cr(III) die charakteristische grüne Farbe.
Tertiäre Alkohole reagieren nicht mit Chrom, und daher wird kein Niederschlag gebildet, wodurch die Lösung orange bleibt. Daher kann der Jones-Test helfen, primäre und sekundäre Alkohole von tertiären Alkoholen zu unterscheiden.
<h4>Lucas Test</h4>
Beim Lucas-Test wird Zink(II)-chlorid in Gegenwart von Salzsäure als Reagenz verwendet. In Gegenwart eines Alkohols halogeniert das Lucas-Reagenz den Alkohol und bildet in wässrigen Lösungen ein unlösliches Produkt. Die Reaktionsgeschwindigkeit dafür ist stark abhängig von der Bildung eines Carbokations, das durch den Verlust des Hydroxyls als Wasser verursacht wird. Eine Carbokation, die durch einen Primäralkohol gebildet wird, ist instabil und tritt daher nicht ohne weiteres auf. Dies führt zu keiner beobachtbaren Reaktion bei Raumtemperatur. Ein tertiärer Alkohol bildet ein stabiles Carbokation, was zu einer schnellen Reaktion auf die Zugabe des Lucas-Reagenzes führt. Dies führt dazu, dass eine zweite Phase im Reaktionsgemisch entsteht, da das halogenierte Endprodukt in Wasser unlöslich ist. Sekundäre Alkohole bilden eine weniger stabile Carbokation als tertiäre Alkohole, aber die Reaktion erfolgt bei Raumtemperatur in wenigen Minuten. Daher kann der Lucas-Test helfen, zwischen primären, sekundären und tertiären Alkoholen zu unterscheiden.
<h4>Referenzen</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>

Identifizierung von Alkoholen

Alkohole
Alkohole sind organische Verbindungen, die zu den bekanntesten und bekanntesten gehören, da sie vielfältige Anwendungen und Verwendungen im Alltag haben ...

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alcohol tests for primary, secondary, and tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary.

Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical behavior instead of relying only on instrument-based methods such as NMR. By combining several qualitative tests, the identity of an alcohol can be determined in a way similar to how aldehydes and ketones are identified.

The ferric chloride test helps tell aromatic alcohols from aliphatic alcohols. Iron(III) chloride starts as a red-orange solution. If an aromatic alcohol such as phenol is present, the chloride atoms are replaced and the solution turns purple. Aliphatic alcohols do not react in this test, so the color stays red-orange.

The Jones test uses chromium trioxide with sulfuric acid as a strong oxidizing reagent. A primary alcohol is oxidized first to an aldehyde and then to a carboxylic acid. A secondary alcohol is oxidized to a ketone. Chromium starts in the +6 oxidation state, which gives the reagent its reddish-orange color, and is reduced to Cr(III), which is green. Tertiary alcohols do not react, so the solution remains orange. This makes the Jones test useful for separating primary and secondary alcohols from tertiary alcohols.

The Lucas test uses zinc(II) chloride in hydrochloric acid. It halogenates the alcohol and produces an insoluble product in water. The test depends on carbocation formation when the hydroxyl group leaves as water. Primary alcohols do not show a visible reaction at room temperature because their carbocations are unstable. Tertiary alcohols react quickly because their carbocations are more stable, and a second layer appears. Secondary alcohols react more slowly and usually take a few minutes. This test helps distinguish primary, secondary, and tertiary alcohols.

Alcohol Tests for Primary, Secondary, and Tertiary

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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.

Alcohol Tests for Primary, Secondary, and Tertiary

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