Name: carbonyl tests for aldehydes and ketones
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 9 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.8

SC.912.P.8.13

identification-of-unknown-aldehydes-and-ketones

Identification of Unknown Aldehydes and Ketones

الألدهيدات والكيتونات لها بنية مماثلة. كلاهما يمتلك مجموعة كربونيل ، وهي عبارة عن كربون مزدوج مرتبط بالأكسجين. يحتوي الألدهيد على هيدروجين واحد على الأقل متصل بالكربونيل الكربوني. المجموعة الثانية هي إما مجموعة هيدروجين أو مجموعة قائمة على الكربون. في المقابل ، يحتوي الكيتون على مجموعتين أساسهما الكربون متصلتين بالكربون الكربوني. يمكن استخدام بعض التفاعلات التي تتعرض لها الألدهيدات والكيتونات للتمييز بينها أو تحديد مجموعاتها الوظيفية بناء على الاختلافات المرئية في نتيجة التفاعل. 
أحد هذه التفاعلات هو اختبار DNPH ، والذي يستخدم لتحديد ما إذا كان الألدهيد أو الكيتون عطريا. في هذا التفاعل ، يهاجم 2،4-ثنائي نيتروفينيل هيدرازين ، أو DNPH ، الكربونيل من الألدهيد أو الكيتون في محلول حمضي مائي. ينتج عن تفاعل التكثيف هذا هيدرازون يترسب من المحلول المائي. 
عندما يتفاعل الكيتون أو الألدهيد غير العطري مع DNPH ، يكون الراسب أصفر. ومع ذلك ، فإن الكيتونات العطرية والألدهيدات تعطي راسب أحمر برتقالي. يمكن أيضا استخدام DNPH لتمييز الكحول والإسترات عن الألدهيدات والكيتونات لأن DNPH لا يتفاعل مع الكحول أو الإسترات. نسمي هذا النقص في رد الفعل نتيجة سلبية. 
يتم استخدام تفاعل مفيد آخر كاختبار يودوفورم لكيتونات الميثيل ، وهي كيتونات تحتوي على ميثيل واحد على الأقل كمجموعة وظيفية. عندما يتم خلط كيتون الميثيل مع اليود في ظل ظروف قلوية مائية ، يحل اليود محل كل هيدروجين ميثيل ، مما يجعل مجموعة مغادرة ممتازة. الاستبدال ، متبوعا بنقل البروتون ، يحول المجموعة المتبقية إلى يودوفورم ، والذي يترسب من المحلول كمادة صلبة صفراء شاحبة. 
يعمل هذا التفاعل أيضا مع الأسيتالديهايد ، وهو ألدهيد مع الميثيل كمجموعة R. يعتمد التفاعل على التفاعل الفريد للهيدروجين في مجموعة ألفا ميثيل ، لذا فإن خلط أي كيتون أو ألدهيد آخر مع اليود لن يصنع يودوفورم أصفر صلب. 
أخيرا ، يمكننا التمييز بين الكيتونات والألدهيدات باستخدام اختبار Tollens. ديامين سيلفر (1+) ، أو كاشف تولينز ، يؤكسد الألدهيدات إلى أحماض الكربوكسيل. يتم تقليل كاشف Tollens إلى عنصر الفضة في هذه العملية ، والتي إما تغطي الجدار الداخلي لأنبوب الاختبار أو تشكل راسب أسود. ومع ذلك ، فإن معظم الكيتونات لا تتأكسد بواسطة كاشف Tollens ، لذلك لن تتشكل الفضة الصلبة. 
في هذا المختبر ، ستحدد العديد من الألدهيدات والكيتونات غير المعروفة عن طريق إجراء اختبار DNPH واختبار Tollens واختبار اليودوفورم.

تحديد الألدهيدات والكيتونات غير المعروفة

<h4>الألدهيدات والكيتونات </h4>
تحتوي الألدهيدات والكيتونات على مجموعة كربونيل (C = O) كمجموعة وظيفية. يحتوي الكيتون على مجموعتين من الألكيل أو الأريل متصلتين بالكربونيل الكربوني (RCOR). أبسط كيتون هو الأسيتون ، الذي يحتوي على مجموعتين من الميثيل متصلين بالكربونيل الكربوني (CH 3 COCH 3 ). 
يشبه الألدهيد الكيتون ، باستثناء أنه بدلا من مجموعتين جانبيتين متصلتين بالكربونيل الكربوني ، لديهم هيدروجين واحد على الأقل (RCOH). أبسط ألدهيد هو الفورمالديهايد (HCOH) ، حيث يحتوي على هيدروجين متصلين بمجموعة الكربونيل. تحتوي جميع الألدهيدات الأخرى على هيدروجين واحد مرتبط بمجموعة الكربونيل ، مثل الجزيء البسيط أسيتالديهايد ، الذي يحتوي على هيدروجين واحد ومجموعة ميثيل واحدة (HCOCH 3 ). 
الكربونيل الكربوني في كل من الألدهيدات والكيتونات محب للكهرباء ، مما يعني أنه يحتوي على ثنائي القطب بسبب الكهربية لذرة الأكسجين المرفقة. هذا يجعل الكربونيل هدفا مثاليا للنوكليوفيلات في تفاعل الإضافة النووية. خلال هذا التفاعل ، يهاجم المحب للنواة ، أو المتبرع بالإلكترون ، الكربونيل لتشكيل الوسيط رباعي السطوح. يقبل الأكسجين سالب الشحنة أيون الهيدروجين لتشكيل مجموعة هيدروكسيل. 
عادة ما تمتلك محبي النواة شحنة سالبة أو زوجا وحيدا على ذرة غير متجانسة ، والتي يمكن أن تتخذ عدة أشكال (OH - ، RO - ، CN - ، R 3 C - ، RNH 2 ، ROH). بالنسبة للأمينات الأولية (RNH 2 ) ، لا يتوقف التفاعل عند تكوين الوسيط رباعي السطوح مع مجموعة هيدروكسيل. بدلا من ذلك ، يحدث تفاعل إقصاء ينتج مجموعة وظيفية مزدوجة الارتباط من الكربون والنيتروجين تعرف باسم إيمين. يوفر فهم التفاعلات التي يمكن أن تمر بها الألدهيدات والكيتونات طريقة للتمييز بين هذه الأنواع من المركبات العضوية المتشابهة. 
<h4>اختبار DNPH</h4>
يتم استغلال تكوين الإيمينات من الكيتونات أو الألدهيدات من خلال استخدام الكاشف 2،4-ثنائي نيتروفينيل هيدرازين (DNPH). في تفاعل الإضافة والقضاء هذا ، تهاجم المجموعة الأمينية الأولية من DNPH الكربونيل الألدهيد أو الكيتون في بيئة حمضية. ينتج عن تفاعل التكثيف تكوين هيدرازون يترسب خارج المحلول. 
تشير الرواسب الصفراء إلى الكيتونات غير المترافقة أو الألدهيدات ، بينما تشير الرواسب الحمراء البرتقالية إلى الأنظمة المترافقة. يستخدم هذا الاختبار للتمييز بين الكيتونات والألدهيدات والكحوليات والإسترات التي لا يتفاعل معها DNPH ، وبالتالي لا يتشكل أي رواسب. مشتقات الكيتون أو الألدهيد هي مواد بلورية ذات نقاط انصهار محددة جيدا ، والتي تم الإبلاغ عنها في الأدبيات ويمكن استخدامها لتحديد المركبات المحددة. 
<h4>اختبار الهالوفورم</h4>
اختبار آخر هو اختبار الهالوفورم ، والذي يستخدم لتحديد ما إذا كان الكيتون هو كيتون الميثيل. تحتوي كيتونات الميثيل على مجموعة ميثيل متصلة بالكربونيل الكربوني (RCOCH 3 ). يمكن أن تكون المجموعة R إما هيدروجين (ميثيل ألدهيد) أو مجموعة ألكيل أو مجموعة أريل. 
تحدث آلية رد الفعل لاختبار الهالوفورم في ظل الظروف الأساسية. أولا ، يخضع الكيتون لتوتومير كيتو إينول. ثم يهاجم الإينولات المحبة للنواة اليود لإعطاء أيون اليود والكيتون المهلجن. يتكرر هذا ما مجموعه ثلاث مرات حتى يتم استبدال جميع الهيدروجينات من مجموعة ميثيل الكيتون باليود. بعد ذلك ، يتفاعل الهيدروكسيد مع مركز الكربونيل الكربوني المحب للكهرباء لتشكيل وسيط رباعي السطوح مع أكسجين سالب الشحنة ، وهو مرتبط أحادي بالكربونيل. عند إصلاح الرابطة المزدوجة C-O ، تترك مجموعة ثلاثي الهالوميثيل كمجموعة مغادرة مستقرة. أخيرا ، يتم إزالة البروتون من حمض الكربوكسيل المتكون بواسطة ثلاثي الميثيل سالب الشحنة لإعطاء الهالوفورم - ثلاثي الهالوميثان - والكربوكسيلات. إذا كان اليود هو الهالوجين ، فسيكون للراسب لون أصفر مميز. سيحدث هذا التفاعل فقط مع كيتونات الميثيل ، وسيعطي نتيجة سلبية لأي مركب آخر يحتوي على الكربونيل. 
<h4>اختبار تولينس</h4>
اختبار Tollens هو تفاعل يستخدم لتمييز الألدهيدات عن الكيتونات ، حيث يمكن أن تتأكسد الألدهيدات إلى حمض كربوكسيلي بينما لا تستطيع الكيتونات. كاشف تولينز ، وهو خليط من نترات الفضة والأمونيا ، يؤكسد الألدهيد إلى حمض الكربوكسيل. يتم تقليل أيون الفضة Ag+ إلى الفضة الصلبة ، Ag(s). تشكل الفضة الصلبة فيلما على الجدار الداخلي لأنبوب الاختبار ، يشبه المرآة الفضية. لا تتفاعل الكيتونات مع كاشف تولين ، وبالتالي لا تؤدي إلى تكوين مرآة فضية على جدران أنبوب الاختبار. 
<h4>المراجع</h4>
<ol>
	<li style="font-size:17px">Streitwieser ، A. ، Heathcock ، C.H. ، Kosower ، E.M. (1998). مقدمة في الكيمياء العضوية. نهر السرج العلوي ، نيوجيرسي: قاعة برنتيس. </li>
	<li style="font-size:17px">فوسون ، آر سي ، بول ، بكالوريوس (1934). رد الفعل الهالوي. المراجعات الكيميائية. 15 (3) ، 275-309. </li>
</ol>

الألدهيدات والكيتونات
تحتوي الألدهيدات والكيتونات على مجموعة كربونيل (C = O) كمجموعة وظيفية. يحتوي الكيتون على مجموعتين من الألكيل أو الأريل متصلة ب ...

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carbonyl tests for aldehydes and ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group.

The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom pulls electron density toward itself. This makes the carbonyl carbon a target for nucleophiles, or electron donors, in a nucleophilic addition reaction. In that reaction, the nucleophile attacks the carbonyl and forms a tetrahedral intermediate. The negatively charged oxygen then accepts a hydrogen ion to form a hydroxyl group. Common nucleophiles can include OH-, RO-, CN-, R3C-, RNH2, and ROH. With primary amines, the reaction continues past the intermediate and can form an imine, which has a carbon-nitrogen double bond.

These reaction patterns help chemists tell similar carbonyl compounds apart. One useful test is the 2,4-dinitrophenylhydrazine, or DNPH, test. In acidic solution, DNPH reacts with an aldehyde or ketone by an addition-elimination process. The result is a hydrazone precipitate. Yellow precipitates usually point to non-conjugated aldehydes or ketones, while red-orange precipitates suggest conjugated systems. Alcohols and esters do not react with DNPH, so no precipitate forms. The crystalline derivatives also have well-defined melting points that can help identify the specific compound.

Another test is the haloform test, which checks whether a ketone is a methyl ketone. A methyl ketone has a methyl group attached to the carbonyl carbon, written as RCOCH3. In basic conditions, the ketone first undergoes keto-enol tautomerization. Then the enolate reacts with iodine until the methyl hydrogens are replaced. After three substitutions, hydroxide reacts again, and the trihalomethyl group leaves. The reaction gives a haloform, which is a trihalomethane, along with a carboxylate. When iodine is used, the precipitate is yellow. This test is negative for carbonyl compounds that are not methyl ketones.

The Tollens test distinguishes aldehydes from ketones. Tollens reagent is a mixture of silver nitrate and ammonia. It oxidizes an aldehyde to a carboxylic acid, while silver ion, Ag+, is reduced to solid silver, Ag(s). The silver coats the inside of the test tube and forms a silver mirror. Ketones do not react with Tollens reagent, so they do not produce this mirror.

Carbonyl Tests for Aldehydes and Ketones

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thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

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,...

synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

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...

identification of unknown aldehydes and ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

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...

chemistry

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

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Learn how DNPH, haloform, and Tollens tests help identify aldehydes and ketones by spotting precipitates, methyl ketones, and the silver mirror.

Carbonyl Tests for Aldehydes and Ketones | JoVE K12

Georgia Standards of Excellence

9-12

SC3.

Indicators of Chemical Reactions

استعد لتدريس تحديد الألدهيدات والكيتونات غير المعروفة من خلال هذا الدليل الإرشادي للمدرسين لمدة 7 دقيقة. يغطي خطوات التحضير الأساسية لمختبر Chemistry على JoVE Lab Manual.

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اتبع إجراءات تحديد الألدهيدات والكيتونات غير المعروفة خطوة بخطوة في فيديو بروتوكول الطالب هذا لمدة 15 دقيقة. جزء من مجموعة Chemistry على JoVE Lab Manual.

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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 ...

molecular-comparison-of-gases-liquids-and-solids

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

physical-and-chemical-properties-of-matter

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. ...

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 ...

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.

Carbonyl Tests for Aldehydes and Ketones

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