The idiom "So X as to (be) Y" is listed in the Manhattan SC Guide (Pg 111).

However, according to OG (Golden book Pg 675) Q#33-explanation of why option C is wrong "the construction so x as to y is not a correct idiom".

OG explanation cannot be wrong. Am I missing something?

SO
So + adverb/ adjective + that
•Among the cossacks, vegetable farming was once so despised that it was forbidden on pain of death.
•He is so happy that
So + that
•Xue Mei spoke so that we would stop asking her questions.
•The sales materials are presented at the end of the meetings so that the participants won't realize the meeting is actually a sales presentation.

SUCH
Such + adjective + noun + that
•It was such a good new that I couldn’t wait to share it with my parents.
•Such changing conditions as seasonal and daily cycles or different planetary
•Such extraordinary fees
Such + noun + as to (noun=way, manner etc)
•Xue Mei spoke in such a way as to calm us down.
•The sales materials are presented in such a way as to encourage attendees to
purchase the products on the spot.
NOTE – such + noun + as to is much less common than so + adj/adv + as to

SUCH X AS Y AND Z

I know our curriculum director recently identified an idiom that he is removing from the list for the next publication of the book - I don't remember if this is it, though. I'll ask him and get back to you!

Yes, this is the idiom you're thinking of, Stacey -- we're going to alter the presentation of the two idioms "so X as to Y" and "X enough to Y" in the next edition of our book. The issue is complex, however.

Recently we have been noting a few examples in which we feel that the Official Guide *explanation* is not so great. This example may be the most egregious, because the OG 11th edition actually contradicts the OG 10th edition on this point!

As you noted, Mpanwar, the OG makes the claim that “the construction 'so X as to Y' is not a correct idiom” (OG #33, 11th edition) in connection with the following sentence:
"... so debilitating is it as to become an economic drain" (OG.33.C)

However, the wholesale rejection of "so X as to Y" is plainly unjustified, as can be seen from the perfectly correct sentences:
- Would you be so kind as to tell me the time? (Swan, "Practical English Usage," Oxford University Press 2005, p. 539)
- Its smell was so foul as to make a lady faint.

The GMAT itself violates the suspect “rule” against the idiom "so X as to Y":
"The Emperor Augustus, it appears, commissioned an idealized sculpture portrait, the features of which are so unrealistic as to constitute what one scholar calls an 'artificial face.'" (OG #88, 10th edition, answer choice A)

Commenting on (A), the OG says “Choice A, which uses the clear, concise, and idiomatic construction 'so unrealistic as to constitute,' is best” (emphasis added).

The difference between the incorrect OG.33.C and the correct examples seems to be that in OG.33.C, the X was a clause ("debilitating is it"), whereas in the correct examples, X was just an adjective. The real issue with OG.33.C is that the word order is unnaturally reversed: "so debilitating is it" should be "it is so debilitating."

So, where does this leave you?

We think the 10th edition was right. You CAN use "so X as to Y" if X is an adjective or adverb. "X enough to Y" is also idiomatic. These two idioms differ *slightly* in meaning, as we discuss in the current edition of our Strategy Guide, but we now feel that it is actually unlikely that the GMAT would force you to choose between these two idioms, if they're both correctly written.

You should, however, avoid "so X as to Y" if X is not an adjective or adverb. The 11th edition *explanation* (that "so X as to Y" is itself "not a correct idiom") seems fallacious to us.

Related idioms: "so [adjective] that" is preferable to "[adjective] enough that."

Again, in the next edition of our Sentence Correction Guide, we're going to clarify these issues. This is the only case we've seen in which one edition of the OG blatantly contradicts another edition, by the way.

You can use so as when

sentence is negative such as

1. so unrealistic as
2. not so much as.

Both example from og 10 . It clears the doubt.

Yes, but you can also use the idiom So X as to Y when the X is postive, such as in the example Chris provided above: "So foul as to make a lady faint." The adjective or adverb inserted as X does not have to be either positive or negative.